Update .gitignore

Author: divadsn

.gitignore

@@ -5,8 +5,9 @@
 *.apk
 *.ap_
 
-# Calculated md5 checksums
+# Drone CI plugin files
 *.md5sum
+changelog.txt
 
 # Files for the ART/Dalvik VM
 *.dex
@@ -63,4 +64,4 @@ fastlane/report.xml
 fastlane/Preview.html
 fastlane/screenshots
 fastlane/test_output
-fastlane/readme.md
+fastlane/readme.md