Updated Travis CI configuration - added PHP7.4 builds

Author: michalbundyra

.travis.yml

@@ -33,13 +33,24 @@ matrix:
         - DEPS=latest
     - php: 7.3
       env:
-      - DEPS=lowest
+        - DEPS=lowest
     - php: 7.3
       env:
-      - DEPS=locked
+        - DEPS=locked
     - php: 7.3
       env:
-      - DEPS=latest
+        - DEPS=latest
+    - php: 7.4snapshot
+      env:
+        - DEPS=lowest
+    - php: 7.4snapshot
+      env:
+        - DEPS=locked
+    - php: 7.4snapshot
+      env:
+        - DEPS=latest
+  allow_failures:
+    - php: 7.4snapshot
 
 before_install:
   - if [[ $TEST_COVERAGE != 'true' ]]; then phpenv config-rm xdebug.ini || return 0 ; fi