improvement(asdf_install): don't break when a plugin is already installed.

asdf_install

@@ -3,6 +3,19 @@
 set -e
 
 source ~/.asdf/asdf.sh
-cat .tool-versions | cut -d \  -f 1 | xargs -n 1 asdf plugin add
+REQUIRED_PLUGINS=$(cat .tool-versions | cut -d \  -f 1)
+INSTALLED_PLUGINS=$(asdf plugin list)
+
+for PLUGIN in $REQUIRED_PLUGINS; do
+  if [[ $INSTALLED_PLUGINS =~ (^|[^[:alpha:]])$PLUGIN([^[:alpha:]]|$) ]]; then
+    echo "ASDF plugin $PLUGIN already installed"
+  else
+    echo "Installing $PLUGIN ASDF plugin..."
+    asdf plugin add $PLUGIN
+    echo "   ...done"
+  fi
+done
+
+echo "Running ASDF install..."
 asdf install
-cat .tool-versions | xargs -n 2 asdf global
+echo "   ...done"