Allow PHP nightly to fail

WyriHaximus · WyriHaximus · commit caf1248c3fd4 · 2018-12-24T13:56:09.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -7,6 +7,8 @@ cache:
 
 ## Build matrix for lowest and highest possible targets
 matrix:
+  allow_failures:
+    - php: nightly
   include:
     - php: 7.2
       env:
