actually depend on graceful-fs

Since graceful-fs doesn't monkey-patch the builtin, there's no need to make
it optional. Also, it's currently being pulled in all the time anyway, so why
not just depend on it normally?

index.js

@@ -11,11 +11,7 @@
 module.exports = cmdShim
 cmdShim.ifExists = cmdShimIfExists
 
-try {
-  var fs = require("graceful-fs")
-} catch (e) {
-  var fs = require("fs")
-}
+var fs = require("graceful-fs")
 
 var mkdir = require("mkdirp")
   , path = require("path")

package.json

@@ -10,9 +10,6 @@
     "url": "https://github.com/ForbesLindesay/cmd-shim.git"
   },
   "license": "BSD",
-  "optionalDependencies": {
-    "graceful-fs": "2"
-  },
   "dependencies": {
     "graceful-fs": "^3.0.2",
     "mkdirp": "~0.5.0"
@@ -21,4 +18,4 @@
     "tap": "~0.4.11",
     "rimraf": "~2.2.8"
   }
-}
+}