Do not use a git submodule for RtAudio, so that always the newest version is chosen

.gitmodules

 [submodule "src/lib/aubio/aubio.git"]
 	path = src/lib/aubio/aubio.git
 	url = https://github.com/aubio/aubio
-[submodule "src/lib/RtAudio/rtaudio"]
-	path = src/lib/RtAudio/rtaudio
-	url = https://github.com/thestk/rtaudio.git

src/lib/RtAudio/.gitignore

-*/*
\ No newline at end of file
+*

src/lib/RtAudio/build_rtAudio.sh

 #!/bin/bash
-
+set -e
 # see https://github.com/thestk/rtaudio/blob/master/install.txt
 
-# add and update git submodule
-git submodule init
-git submodule update
-# cd into git repo
 GIT_DIR=rtaudio
-cd $GIT_DIR
+# add or update git
+if [ ! -d "$GIT_DIR" ]; then # if folder "GIT_DIR" does not exists
+  git clone https://github.com/thestk/rtaudio.git "$GIT_DIR"
+  cd "$GIT_DIR"
+else
+  cd "$GIT_DIR"
+  if [[ $(git pull) = "Already up to date." ]]; then
+    # we can skip recompiling, because the last build is already up to date
+    echo "Already up to date."
+    exit 0
+  fi
+fi
+# we are in the "$GIT_DIR" now
+
 # build
 if [[ "$OSTYPE" == "msys" ]] || ! [[ -z "$GITLAB_CI" ]]; then
     # we are on windows or on the gitlab ci

rtaudio @ 57c2c9d7

-Subproject commit 57c2c9d7598a783a5167422cd744f4d3797141bb