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
Change-Id: I02f4069bca8f8db8d02773e1239f42d4cd52bb24

Android.mk

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)