Travis: use carla instead of carla-git

Due to some breaking changes in the development branch of Carla,
we can't use the package right now.
Fortunately, the carla package now points to 2.0 series. So we will use it.

See also: https://kx.studio/News/?action=view&url=changes-in-kxstudio-repos-regarding-carla-and-jack2

.travis/linux..install.sh

@@ -22,4 +22,4 @@ sudo apt-get install -y $PACKAGES
 sudo add-apt-repository -y ppa:kxstudio-debian/libs
 sudo add-apt-repository -y ppa:kxstudio-debian/apps
 sudo apt-get update
-sudo apt-get install -y carla-git
+sudo apt-get install -y carla