tools/install: Accept the repository URL through env "OSH_REPOSITORY"

tools/install.sh

@@ -230,6 +230,10 @@ _omb_install_main() {
     OSH=~/.oh-my-bash
   fi
 
+  if [[ ! $OSH_REPOSITORY ]]; then
+    OSH_REPOSITORY=https://github.com/ohmybash/oh-my-bash.git
+  fi
+
   # Only enable exit-on-error after the non-critical colorization stuff,
   # which may fail on systems lacking tput or terminfo
 
@@ -261,7 +265,7 @@ _omb_install_main() {
       return 1
     fi
   fi
-  _omb_install_run git clone --depth=1 https://github.com/ohmybash/oh-my-bash.git "$OSH" || {
+  _omb_install_run git clone --depth=1 "$OSH_REPOSITORY" "$OSH" || {
     printf "Error: git clone of oh-my-bash repo failed\n"
     return 1
   }