[SPARK-8900] [SPARKR] Fix sparkPackages in init documentation

cc pwendell

Author: Shivaram Venkataraman <shivaram@cs.berkeley.edu>

Closes #7293 from shivaram/sparkr-packages-doc and squashes the following commits:

c91471d [Shivaram Venkataraman] Fix sparkPackages in init documentation

docs/sparkr.md

@@ -68,7 +68,7 @@ you can specify the packages with the `packages` argument.
 
 <div data-lang="r" markdown="1">
 {% highlight r %}
-sc <- sparkR.init(packages="com.databricks:spark-csv_2.11:1.0.3")
+sc <- sparkR.init(sparkPackages="com.databricks:spark-csv_2.11:1.0.3")
 sqlContext <- sparkRSQL.init(sc)
 {% endhighlight %}
 </div>