[MINOR] [SPARKR] Fix some validation problems in SparkR

Getting rid of some validation problems in SparkR
https://github.com/apache/spark/pull/7883

cc shivaram

```
inst/tests/test_Serde.R:26:1: style: Trailing whitespace is superfluous.

^~
inst/tests/test_Serde.R:34:1: style: Trailing whitespace is superfluous.

^~
inst/tests/test_Serde.R:37:38: style: Trailing whitespace is superfluous.
  expect_equal(class(x), "character")
                                     ^~
inst/tests/test_Serde.R:50:1: style: Trailing whitespace is superfluous.

^~
inst/tests/test_Serde.R:55:1: style: Trailing whitespace is superfluous.

^~
inst/tests/test_Serde.R:60:1: style: Trailing whitespace is superfluous.

^~
inst/tests/test_sparkSQL.R:611:1: style: Trailing whitespace is superfluous.

^~
R/DataFrame.R:664:1: style: Trailing whitespace is superfluous.

^~~~~~~~~~~~~~
R/DataFrame.R:670:55: style: Trailing whitespace is superfluous.
                df <- data.frame(row.names = 1 : nrow)
                                                      ^~~~~~~~~~~~~~~~
R/DataFrame.R:672:1: style: Trailing whitespace is superfluous.

^~~~~~~~~~~~~~
R/DataFrame.R:686:49: style: Trailing whitespace is superfluous.
                    df[[names[colIndex]]] <- vec
                                                ^~~~~~~~~~~~~~~~~~
```

Author: Yu ISHIKAWA <yuu.ishikawa@gmail.com>

Closes #8474 from yu-iskw/minor-fix-sparkr.

R/pkg/R/DataFrame.R

@@ -661,15 +661,15 @@ setMethod("collect",
               # listCols is a list of columns
               listCols <- callJStatic("org.apache.spark.sql.api.r.SQLUtils", "dfToCols", x@sdf)
               stopifnot(length(listCols) == ncol)
-              
+
               # An empty data.frame with 0 columns and number of rows as collected
               nrow <- length(listCols[[1]])
               if (nrow <= 0) {
                 df <- data.frame()
               } else {
-                df <- data.frame(row.names = 1 : nrow)                
+                df <- data.frame(row.names = 1 : nrow)
               }
-              
+
               # Append columns one by one
               for (colIndex in 1 : ncol) {
                 # Note: appending a column of list type into a data.frame so that
@@ -683,7 +683,7 @@ setMethod("collect",
                   # TODO: more robust check on column of primitive types
                   vec <- do.call(c, col)
                   if (class(vec) != "list") {
-                    df[[names[colIndex]]] <- vec                  
+                    df[[names[colIndex]]] <- vec
                   } else {
                     # For columns of complex type, be careful to access them.
                     # Get a column of complex type returns a list.

R/pkg/inst/tests/test_Serde.R

@@ -23,7 +23,7 @@ test_that("SerDe of primitive types", {
   x <- callJStatic("SparkRHandler", "echo", 1L)
   expect_equal(x, 1L)
   expect_equal(class(x), "integer")
-  
+
   x <- callJStatic("SparkRHandler", "echo", 1)
   expect_equal(x, 1)
   expect_equal(class(x), "numeric")
@@ -31,10 +31,10 @@ test_that("SerDe of primitive types", {
   x <- callJStatic("SparkRHandler", "echo", TRUE)
   expect_true(x)
   expect_equal(class(x), "logical")
-  
+
   x <- callJStatic("SparkRHandler", "echo", "abc")
   expect_equal(x, "abc")
-  expect_equal(class(x), "character")  
+  expect_equal(class(x), "character")
 })
 
 test_that("SerDe of list of primitive types", {
@@ -47,17 +47,17 @@ test_that("SerDe of list of primitive types", {
   y <- callJStatic("SparkRHandler", "echo", x)
   expect_equal(x, y)
   expect_equal(class(y[[1]]), "numeric")
-  
+
   x <- list(TRUE, FALSE)
   y <- callJStatic("SparkRHandler", "echo", x)
   expect_equal(x, y)
   expect_equal(class(y[[1]]), "logical")
-  
+
   x <- list("a", "b", "c")
   y <- callJStatic("SparkRHandler", "echo", x)
   expect_equal(x, y)
   expect_equal(class(y[[1]]), "character")
-  
+
   # Empty list
   x <- list()
   y <- callJStatic("SparkRHandler", "echo", x)

R/pkg/inst/tests/test_sparkSQL.R

@@ -608,7 +608,7 @@ test_that("subsetting", {
   df4 <- df[df$age %in% c(19, 30), 1:2]
   expect_equal(count(df4), 2)
   expect_equal(columns(df4), c("name", "age"))
-  
+
   df5 <- df[df$age %in% c(19), c(1,2)]
   expect_equal(count(df5), 1)
   expect_equal(columns(df5), c("name", "age"))