Increase severity of DefaultCharset to ERROR

Change-Id: I7c7e677d36184a6b908da4ad6aa02fd9d2155919

tools/BUILD

diff --git a/tools/BUILD b/tools/BUILD
index 6765f24..00f2cbe 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -31,7 +31,7 @@
         "-Xep:CannotMockFinalClass:WARN",
         "-Xep:ClassCanBeStatic:WARN",
         "-Xep:ClassNewInstance:WARN",
-        "-Xep:DefaultCharset:WARN",
+        "-Xep:DefaultCharset:ERROR",
         "-Xep:DoubleCheckedLocking:WARN",
         "-Xep:ElementsCountedInLoop:WARN",
         "-Xep:EqualsHashCode:WARN",