Ignore the Yarn error log

kauhat · web-flow · commit 12db5051228e · 2017-07-04T15:25:06.000+01:00
Like the npm error log, this file can also be ignored. [See also](https://stackoverflow.com/questions/42592168/should-i-add-yarn-error-log-to-my-gitignore-file)
diff --git a/.gitignore b/.gitignore
@@ -8,4 +8,5 @@
 Homestead.json
 Homestead.yaml
 npm-debug.log
+yarn-error.log
 .env
