Revert "Revert "Change the default for LOCAL_JAVA_LANGUAGE_VERSION from 1.7 to 1.8""

This reverts commit 799d603029701fd565538ed7d09be3cdf34dded9.
diff --git a/core/java_common.mk b/core/java_common.mk
index b88bfe4..59f473c 100644
--- a/core/java_common.mk
+++ b/core/java_common.mk
@@ -4,7 +4,7 @@
 ## Java version
 ###########################################################
 ifeq (,$(LOCAL_JAVA_LANGUAGE_VERSION))
-  LOCAL_JAVA_LANGUAGE_VERSION := 1.7
+  LOCAL_JAVA_LANGUAGE_VERSION := 1.8
 endif
 LOCAL_JAVACFLAGS += -source $(LOCAL_JAVA_LANGUAGE_VERSION) -target $(LOCAL_JAVA_LANGUAGE_VERSION)