Merge pull request #2 from shweta-code/master

Changes to toStrig method in Coordinates Class . StringBuilder to be used instead of StringBuffer since it has a better performance in an environment that doesn't demand multithreaded capabilities.

src/com/thoughtworks/rover/universe/Coordinates.java

@@ -16,7 +16,7 @@ public Coordinates newCoordinatesFor(final int xCoordinateStepValue, final int y
 
     @Override
     public String toString() {
-        StringBuffer coordinateOutput = new StringBuffer();
+        StringBuilder coordinateOutput = new StringBuilder();
         coordinateOutput.append(xCoordinate);
         coordinateOutput.append(" ");
         coordinateOutput.append(yCoordinate);