Fix security vulnerability in checkstyle / guava

Author: TobiGr

app/build.gradle

@@ -93,7 +93,7 @@ android {
 
 ext {
     icepickVersion = '3.2.0'
-    checkstyleVersion = '8.37'
+    checkstyleVersion = '8.38'
     stethoVersion = '1.5.1'
     leakCanaryVersion = '2.5'
     exoPlayerVersion = '2.11.8'