[SPARK-12211][DOC][GRAPHX] Fix version number in graphx doc for migration from 1.1
[SPARK-12211][DOC][GRAPHX] Fix version number in graphx doc for migration from 1.1

Migration from 1.1 section added to the GraphX doc in 1.2.0 (see https://spark.apache.org/docs/1.2.0/graphx-programming-guide.html#migrating-from-spark-11) uses \{{site.SPARK_VERSION}} as the version where changes were introduced, it should be just 1.2.

Author: Andrew Ray <ray.andrew@gmail.com>

Closes #10206 from aray/graphx-doc-1.1-migration.

(cherry picked from commit 7a8e587dc04c2fabc875d1754eae7f85b4fba6ba)
Signed-off-by: Joseph K. Bradley <461476587780aa9fa5611ea6dc3912c146a91760@databricks.com>

haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark,haowu80s/spark