Travis conf didn't match schema

- PHP versions need to be strings
- https://docs.travis-ci.com/user/notifications/#configuring-email-notifications

Also: tell editors like PhpStorm how the YAML needs to be formatted.

.travis.yml

@@ -1,12 +1,12 @@
 language: php
 
 php:
-  - 7.3
-  - 7.2
-  - 7.1
-  - 7.0
-  - 5.6
-  - 5.5
+  - '7.3'
+  - '7.2'
+  - '7.1'
+  - '7.0'
+  - '5.6'
+  - '5.5'
 
 before_install:
   - composer update
@@ -18,6 +18,7 @@ script:
 
 notifications:
   email:
-    - will.knauss@gmail.com
-  on_success: never
-  on_failure: always
+    recipients:
+      - will.knauss@gmail.com
+    on_success: never
+    on_failure: always