feat(install): allow local installs to specify version

closes #423
- `ghost install 1.x.x --local` now works for local installs

Author: acburdine

lib/commands/install.js

@@ -41,9 +41,11 @@ class InstallCommand extends Command {
 
         let local = false;
 
-        if (version === 'local') {
+        // If command is `ghost install local`, or command is
+        // `ghost install 1.x.x --local`, do a local install
+        if (version === 'local' || argv.local) {
             local = true;
-            version = null;
+            version = (version === 'local') ? null : version;
             this.system.setEnvironment(true, true);
         }