Upgrade ruby to 2.7.7 following failed build

NTerpo · NTerpo · commit 57c2c8da61e7 · 2023-01-10T15:56:07.000+01:00
diff --git a/.travis.yml b/.travis.yml
@@ -1,7 +1,7 @@
 sudo: false
 language: ruby
 rvm:
-  - 2.4.2
+  - 2.7.7
 cache: bundler
 env:
   global:
