Requires JDK 8

This change deprecate JDK 7 as JavaBuilder follow changes in Java 9
and might use Java 8 features. We will maintain a build with the
JDK 7 as long as possible but this build won't include updates
in JavaBuilder.

RELNOTES[INC]: Bazel requires JDK 8 to run.

--
MOS_MIGRATED_REVID=103069207
diff --git a/tools/jdk/BUILD b/tools/jdk/BUILD
index 2ee3d68..3326081 100644
--- a/tools/jdk/BUILD
+++ b/tools/jdk/BUILD
@@ -90,8 +90,8 @@
     name = "toolchain",
     encoding = "UTF-8",
     jvm_opts = ["-client"],
-    source_version = "7",
-    target_version = "7",
+    source_version = "8",
+    target_version = "8",
 )
 
 exports_files([