change git fetch alias

Tragically, running `tags` and `prune` together makes git prune all branches. do
two fetches till this is resolved (if it will ever be).

zsh/omz-custom/git.zsh

@@ -7,7 +7,7 @@ alias gd='git diff'
 alias gds='git diff --staged'
 
 alias gcob='git checkout -b'
-alias gf='git fetch --tags --prune'
+alias gf='git fetch --tags && git fetch --prune'
 
 alias gbd='git branch -D'