Fix broken build on OTP-18

New version of "elvis" doesn't support OTP-18

.travis.yml

@@ -11,13 +11,13 @@ install: "true"
 language: erlang
 matrix:
   include:
-    - otp_release: 22.0
+    - otp_release: 22.2
     - otp_release: 21.3
     - otp_release: 20.3
     - otp_release: 19.3
     - otp_release: 18.3
       dist: trusty
 script:
-  - make elvis
+  - '[ "$TRAVIS_OTP_RELEASE" = "18.3" ] || make elvis' # TODO: remove the guard when OTP18 support is dropped
   - make test
   - make dialyzer