Downgrade grunt-shell to 1.x

2.x requires Node.js 0.12 or newer.

README.md

@@ -128,7 +128,7 @@ your code using Grunt.
 
 ## Release History
 
- * 2017-02-23   v0.4.4   Update dependencies
+ * 2017-02-23   v0.4.6   Update dependencies
  * 2016-12-19   v0.4.3   Add --format to be able to select between PNG
                          and SVG (thanks, Emanuele Aina)
  * 2016-26-08   v0.3.0   Upgrade to Grunt 1.x

package.json

@@ -1,7 +1,7 @@
 {
   "name": "nomnoml-cli",
   "description": "Generates images from nomnoml diagram sources on the command line",
-  "version": "0.4.4",
+  "version": "0.4.6",
   "homepage": "https://github.com/prantlf/nomnoml-cli",
   "author": {
     "name": "Ferdinand Prantl",
@@ -47,7 +47,7 @@
     "grunt-contrib-nodeunit": "^1.0.0",
     "grunt-coveralls": "^1.0.1",
     "grunt-istanbul": "^0.7.2",
-    "grunt-shell": "^2.1.0",
+    "grunt-shell": "^1.3.1",
     "jshint-stylish": "^2.2.1",
     "load-grunt-tasks": "^3.5.2",
     "time-grunt": "^1.4.0"