Add Nextcloud 15 support

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

.travis.yml

@@ -30,6 +30,8 @@ env:
 
 matrix:
   include:
+    - php: 7.2
+      env: "CORE_BRANCH=stable14"
     - php: 7.0
       env: "DB=mysql PHP_COVERAGE=TRUE"
     - php: 7.1

appinfo/info.xml

@@ -18,7 +18,7 @@
 
 	<dependencies>
 		<php min-version="7.0" max-version="7.2"></php>
-		<nextcloud min-version="14" max-version="14" />
+		<nextcloud min-version="14" max-version="15" />
 	</dependencies>
 
 	<two-factor-providers>