Revert "Temporarily force the engine version to 3.3, revert this commit on master, when the SDK has a v3.3 branch."

This reverts commit 56cdc94e55a18b4b05bf8e77467db08802c6d491.

build_engine.sh

@@ -8,8 +8,7 @@ if [ ! -d "engine" ]; then
         # Extract the engine version from the sdk branch tag.
         git clone -b $(echo "$TRAVIS_TAG" | sed -n 's/\(v.\+\)-sdk.\+/\1/p') --single-branch --depth 10 https://github.com/jMonkeyEngine/jMonkeyEngine/ engine # single-branch requires git > 1.7.10, if you see an error, just leave it out.
     else
-        #git clone -b master --single-branch --depth 10 https://github.com/jMonkeyEngine/jMonkeyEngine/ engine # single-branch requires git > 1.7.10, if you see an error, just leave it out.
-        git clone -b v3.3 --single-branch --depth 10 https://github.com/jMonkeyEngine/jMonkeyEngine/ engine # single-branch requires git > 1.7.10, if you see an error, just leave it
+        git clone -b master --single-branch --depth 10 https://github.com/jMonkeyEngine/jMonkeyEngine/ engine # single-branch requires git > 1.7.10, if you see an error, just leave it out.
     fi
     cd engine
 else