Pin libraries needed by vogar tool to java 1.7

vogar still uses javac/dx by default. dx does not
handle v52 class files. The default java version
is going to switch to 1.8. This change pins the
targets need by vogar to 1.7.

Bug: 26753820
Bug: 27310428
(cherry picked from commit 8238dc2d015b4d44bdac5c9a25befdd42eae0663)

Change-Id: Id40b5d2fe475b5ca50162b75f018b31a98cddf4f
diff --git a/Android.mk b/Android.mk
index c29ccce..f1fbc53 100644
--- a/Android.mk
+++ b/Android.mk
@@ -37,4 +37,5 @@
 LOCAL_SRC_FILES := $(apache-commons-math_src_files)
 LOCAL_JAVACFLAGS := -encoding UTF-8
 LOCAL_SDK_VERSION := current
+LOCAL_JAVA_LANGUAGE_VERSION := 1.7
 include $(BUILD_HOST_JAVA_LIBRARY)