add shell script and modify gulp setup

Author: Alban Bailly

dev_setup.sh

@@ -0,0 +1,5 @@
+if
+  cd themes/linode-hugo-theme; then
+  git pull origin development; else
+  cd themes/ && git clone [email protected]:linode/linode-hugo-theme.git; 
+fi

gulpfile.js

@@ -4,7 +4,7 @@ var runSequence = require('run-sequence');
 
 gulp.task('get-base-theme', 
   shell.task(
-    'cd themes/linode-hugo-theme && git pull origin development',
+    './dev_setup.sh',
   )
 );