convert 2 spaces to 4 spaces

contracts/mocks/CounterImpl.sol

@@ -4,18 +4,18 @@ import "../drafts/Counter.sol";
 
 
 contract CounterImpl {
-  using Counter for Counter.Counter;
+    using Counter for Counter.Counter;
 
-  uint256 public theId;
+    uint256 public theId;
 
-  // use whatever key you want to track your counters
-  mapping(string => Counter.Counter) private _counters;
+    // use whatever key you want to track your counters
+    mapping(string => Counter.Counter) private _counters;
 
-  function doThing(string key)
-    public
-    returns (uint256)
-  {
-    theId = _counters[key].next();
-    return theId;
-  }
+    function doThing(string key)
+        public
+        returns (uint256)
+    {
+        theId = _counters[key].next();
+        return theId;
+    }
 }