[MINOR] Use <= for clarity in Pi examples' Monte Carlo process

## What changes were proposed in this pull request?

If my understanding is correct we should be rather looking at closed disk than the opened one.
## How was this patch tested?

Run simple comparison, of the mean squared error of approaches with closed and opened disk.
https://gist.github.com/mrydzy/1cf0e5c316ef9d6fbd91426b91f1969f
The closed one performed slightly better, but the tested sample wasn't too big, so I rely mostly on the algorithm  understanding.

Author: Maria Rydzy <majrydzy+gh@gmail.com>

Closes #15687 from mrydzy/master.

examples/src/main/java/org/apache/spark/examples/JavaSparkPi.java

@@ -54,7 +54,7 @@ public final class JavaSparkPi {
       public Integer call(Integer integer) {
         double x = Math.random() * 2 - 1;
         double y = Math.random() * 2 - 1;
-        return (x * x + y * y < 1) ? 1 : 0;
+        return (x * x + y * y <= 1) ? 1 : 0;
       }
     }).reduce(new Function2<Integer, Integer, Integer>() {
       @Override

examples/src/main/python/pi.py

@@ -38,7 +38,7 @@ if __name__ == "__main__":
     def f(_):
         x = random() * 2 - 1
         y = random() * 2 - 1
-        return 1 if x ** 2 + y ** 2 < 1 else 0
+        return 1 if x ** 2 + y ** 2 <= 1 else 0
 
     count = spark.sparkContext.parallelize(range(1, n + 1), partitions).map(f).reduce(add)
     print("Pi is roughly %f" % (4.0 * count / n))

examples/src/main/scala/org/apache/spark/examples/LocalPi.scala

@@ -26,7 +26,7 @@ object LocalPi {
     for (i <- 1 to 100000) {
       val x = random * 2 - 1
       val y = random * 2 - 1
-      if (x*x + y*y < 1) count += 1
+      if (x*x + y*y <= 1) count += 1
     }
     println("Pi is roughly " + 4 * count / 100000.0)
   }

examples/src/main/scala/org/apache/spark/examples/SparkPi.scala

@@ -34,7 +34,7 @@ object SparkPi {
     val count = spark.sparkContext.parallelize(1 until n, slices).map { i =>
       val x = random * 2 - 1
       val y = random * 2 - 1
-      if (x*x + y*y < 1) 1 else 0
+      if (x*x + y*y <= 1) 1 else 0
     }.reduce(_ + _)
     println("Pi is roughly " + 4.0 * count / (n - 1))
     spark.stop()