Don't ignore tmp and log directory (#2999)

https://weblog.rubyonrails.org/2019/3/13/Rails-4-2-5-1-5-1-6-2-have-been-released/
Rails `5.2.2.1` requires `tmp` directory committed to git repository for CI to run successfully.

Author: okuramasafumi

Rails.gitignore

@@ -1,8 +1,6 @@
 *.rbc
 capybara-*.html
 .rspec
-/log
-/tmp
 /db/*.sqlite3
 /db/*.sqlite3-journal
 /public/system
@@ -12,6 +10,12 @@ capybara-*.html
 rerun.txt
 pickle-email-*.html
 
+# Ignore all logfiles and tempfiles.
+/log/*
+/tmp/*
+!/log/.keep
+!/tmp/.keep
+
 # TODO Comment out this rule if you are OK with secrets being uploaded to the repo
 config/initializers/secret_token.rb
 config/master.key
@@ -59,4 +63,4 @@ yarn-debug.log*
 
 # Ignore uploaded files in development
 /storage/*
-!/storage/.keep
+!/storage/.keep