Ignore .log files

Logs like yarn-error.log can be committed by default but shouldn't.

Change-Id: I583525aec3be573ab51fa6ca742c5a18da6eea7c
(cherry picked from commit f38be8c909d3a839206d9c739f8ff0095cdcca29)
diff --git a/.gitignore b/.gitignore
index 93c1339..3a5d28b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 # Keep following lines sorted according to `LC_COLLATE=C sort`
 *.eml
 *.iml
+*.log
 *.pyc
 *.sublime-*
 *.swp