Fix typo in branch name

Author: martignoni

.travis.yml

@@ -25,7 +25,7 @@ env:
     - MOODLE_BRANCH=MOODLE_37_STABLE DB=mysqli
     - MOODLE_BRANCH=MOODLE_38_STABLE DB=mysqli
     - MOODLE_BRANCH=MOODLE_39_STABLE DB=mysqli
-    - MOODLE_BRANCH=MOODLE_10_STABLE DB=mysqli
+    - MOODLE_BRANCH=MOODLE_310_STABLE DB=mysqli
     - MOODLE_BRANCH=master DB=mysqli
 
 jobs: