Enable lint stacktraces.

Lint sometimes crashes and we need good logs when it does.

Test: None
Change-Id: I5054008a6fdc1a5d8cd3ac81bd3188f011aa3515

diff --git a/gradlew b/gradlew
index a096da0..1516daaa 100755
--- a/gradlew
+++ b/gradlew

@@ -10,6 +10,7 @@
 
 if [ -n "$OUT_DIR" ] ; then
     export GRADLE_USER_HOME="$OUT_DIR/.gradle"
+    export LINT_PRINT_STACKTRACE=true
 fi
 
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