Lock signature_pad version.

Author: Chris Henderson

composer.json

@@ -25,7 +25,7 @@
     "symfony/intl": "^2.7",
     "symfony/yaml": "^2.8",
     "bower-asset/font-awesome": "^4.3",
-    "bower-asset/signature_pad": "^1.5",
+    "bower-asset/signature_pad": "1.5.3",
 	"bower-asset/bootbox.js": "4.4.0"
   },
   "require-dev": {