Use exact version of Ruby 2.4.0 in Travis CI.

For some reason RVM refuses to install relative version 2.4 :(
RhysStansfield · Dec 27, 2016 · c81b7f1 · c81b7f1
1 parent c10b1c2
commit c81b7f1
Showing 1 changed file with 1 addition and 1 deletion.
diff --git a/.travis.yml b/.travis.yml
@@ -5,5 +5,5 @@ rvm:
   - 2.1
   - 2.2
   - 2.3
-  - 2.4
+  - 2.4.0
   - jruby-19mode