Pin to gulp-sourcemaps 1.x

Gulp-sourcemaps 2.x requires node 4 or later, so pin to 1.x to maintain
compatibility with 0.10.

Author: richvdh

package.json

@@ -55,7 +55,7 @@
     "gulp-istanbul": "^0.5.0",
     "gulp-jshint": "^1.9.0",
     "gulp-mocha": "^2.0.0",
-    "gulp-sourcemaps": "^2.2.0",
+    "gulp-sourcemaps": "^1.0.0",
     "http-server": "^0.8.0",
     "jshint-stylish": "^1.0.1",
     "karma": "^0.13.0",