Hugo: Add new .hugo_build.lock

Version 0.89.0 of Hugo creates a new `.hugo_build.lock` lock file
when building the site.

The release notes suggest adding this to the `.gitignore`:
https://github.com/gohugoio/hugo/releases/tag/v0.89.0

community/Golang/Hugo.gitignore

@@ -6,3 +6,6 @@
 hugo.exe
 hugo.darwin
 hugo.linux
+
+# Temporary lock file while building
+/.hugo_build.lock