Lock covert to v1.0.0.

Per https://github.com/substack/covert/issues/9

Author: ljharb

package.json

@@ -28,7 +28,7 @@
     "devDependencies": {
         "tape": "~3.0.1",
         "testling": "~1.7.1",
-        "covert": "~1.0.0",
+        "covert": "1.0.0",
         "jscs": "~1.7.3"
     },
     "license": "MIT",