Removing a wrong validation check

`bin` property of package.json must point to a binary that will
be copied by NPM into the NPM Installation's bin directory. This check
was assuming users would point to a directory containing the binary and
not the binary itself

example/package.json

@@ -7,7 +7,7 @@
     "install": "go-npm"
   },
   "bin": {
-    "myBinaryName": "./bin"
+    "anyCommandNameYouLike": "./bin/myBinaryName"
   },
   "goBinary": {
     "name": "myBinaryName",