Refactor String extension

To add fileString method that it will be in charge of return the file as string.

Author: Rafael da Silva Ferreira

JSONStub.podspec

@@ -8,7 +8,7 @@
 
 Pod::Spec.new do |s|
   s.name             = 'JSONStub'
-  s.version          = '0.1.3'
+  s.version          = '0.1.4'
   s.summary          = 'Use JSONStub to easily load JSON files into your Mappable objects.'
 
 # This description is used to generate tags and improve search results.

JSONStub/Classes/String.swift

@@ -22,6 +22,12 @@ public extension String {
         return json as? [String: AnyObject]
     }
 
+    func fileString() -> String {
+        guard let data = fileData(), let json = String.init(data: data, encoding: .utf8) else { return "{}" }
+
+        return json
+    }
+
     func filePath() -> String? {
         guard splitAtDot.count == 2 else { return nil }