Update BuildEngine to also build the Beta3 Version

build_engine.sh

@@ -3,7 +3,7 @@
 # Also if you want to revert to releases and bintray builds, you need to uninstall them from your local maven repo...
 echo "Downloading the Engine, this may take some time"
 # To have the latest Commit on 3.1 use "-b v3.1". If you want a certain tag, use "-b v3.1.0-beta2"
-git clone -b v3.1.0-beta2 --single-branch --depth 1 http://github.com/jMonkeyEngine/jMonkeyEngine/ engine # single-branch requires git > 1.7.10, if you see an error, just leave it out.
+git clone -b v3.1.0-beta3 --single-branch --depth 1 http://github.com/jMonkeyEngine/jMonkeyEngine/ engine # single-branch requires git > 1.7.10, if you see an error, just leave it out.
 cd engine
 # git checkout tags/v3.1.0-beta2 # To use this, leave out depth and change -b to a branch.
 
@@ -13,4 +13,4 @@ cd engine
 echo "Building the Engine and installing them to your local maven repo...."
 ./gradlew install # Depends on jarJavadoc, jarSourcecode, assemble, dist etc.
 
-cd ../
+cd ../