Test against master again

Now that the requirement was updated to 15 it is necessary to test again
against current master.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

.drone.yml

@@ -17,7 +17,7 @@ pipeline:
     image: nextcloudci/php7.0:php7.0-19
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
       - DB=sqlite
     commands:
       # Pre-setup steps
@@ -35,7 +35,7 @@ pipeline:
     image: nextcloudci/php7.0:php7.0-19
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
       - DB=sqlite
     commands:
       # Pre-setup steps
@@ -51,7 +51,7 @@ pipeline:
     image: nextcloudci/php7.0:php7.0-19
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
       - DB=sqlite
     commands:
       # Pre-setup steps
@@ -67,7 +67,7 @@ pipeline:
     image: nextcloudci/php7.0:php7.0-19
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
       - DB=sqlite
     commands:
       # Pre-setup steps
@@ -87,7 +87,7 @@ pipeline:
     image: nextcloudci/php7.1:php7.1-16
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
       - DB=sqlite
     commands:
       # Pre-setup steps
@@ -107,7 +107,7 @@ pipeline:
     image: nextcloudci/php7.2:php7.2-12
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
       - DB=sqlite
     commands:
       # Pre-setup steps
@@ -127,7 +127,7 @@ pipeline:
     image: nextcloudci/php7.1:php7.1-16
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
     commands:
       # Pre-setup steps
       - wget https://raw.githubusercontent.com/nextcloud/travis_ci/master/before_install.sh
@@ -155,7 +155,7 @@ pipeline:
     image: nextcloudci/acceptance-php7.1:acceptance-php7.1-2
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
     commands:
       # Pre-setup steps
       - git clone --depth 1 -b $CORE_BRANCH https://github.com/nextcloud/server ../server
@@ -173,7 +173,7 @@ pipeline:
     image: nextcloudci/acceptance-php7.1:acceptance-php7.1-2
     environment:
       - APP_NAME=spreed
-      - CORE_BRANCH=stable14
+      - CORE_BRANCH=master
     commands:
       # Pre-setup steps
       - git clone --depth 1 -b $CORE_BRANCH https://github.com/nextcloud/server ../server