Fix a file name in the README.

README.md

@@ -53,7 +53,7 @@ This section assumes that you're using the command-line version of Git.
 
 #### Compile LunatriusCore
 1. Execute `gradlew setupDevWorkspace`. This sets up Forge and downloads the necessary libraries to build LunatriusCore. This might take some time, be patient.
-    * You will generally only have to do this once until the Forge version in `build.properties` changes.
+    * You will generally only have to do this once until the Forge version in `gradle.properties` changes.
 2. Execute `gradlew build`. If you did everything right, `BUILD SUCCESSFUL` will be displayed after it finishes. This should be relatively quick.
     * If you see `BUILD FAILED`, check the error output (it should be right around `BUILD FAILED`), fix everything (if possible), and try again.
 3. Go to `mcdev\LunatriusCore\build\libs`.