Use guava 21.0

guava 20.0 is being removed.

Test: m -j checkbuild
Change-Id: I48ac4f641da3567985339c061dad5d60829aeee0
diff --git a/tools/locked_region_code_injection/Android.mk b/tools/locked_region_code_injection/Android.mk
index d921783..77d5163 100644
--- a/tools/locked_region_code_injection/Android.mk
+++ b/tools/locked_region_code_injection/Android.mk
@@ -10,6 +10,6 @@
     asm-commons-5.2 \
     asm-tree-5.2 \
     asm-analysis-5.2 \
-    guava-20.0 \
+    guava-21.0 \
 
 include $(BUILD_HOST_JAVA_LIBRARY)