.travis.yml: hoisted out spec-on-old-ruby

.travis.yml

@@ -360,27 +360,25 @@ env:
         -Wunused-variable'
       - LDFLAGS=-Wno-unused-command-line-argument
 
-  - &rubyspec25
-    name: Check ruby/spec version guards on Ruby 2.5
+  - &spec-on-old-ruby
     language: ruby
-    rvm: 2.5.7
     before_install:
     install:
     before_script: chmod -R u+w spec/ruby
     # -j randomly hangs.
     script: ruby -C spec/ruby ../mspec/bin/mspec .
+
+  - &rubyspec25
+    name: Check ruby/spec version guards on Ruby 2.5
+    rvm: 2.5.7
+    <<: *spec-on-old-ruby
     after_failure:
       - echo "ruby/spec failed on Ruby 2.5. This is likely because of a missing ruby_version_is guard, please add it. See spec/README.md."
 
   - &rubyspec27
     name: Check ruby/spec version guards on Ruby 2.7
-    language: ruby
     rvm: 2.7.0
-    before_install:
-    install:
-    before_script: chmod -R u+w spec/ruby
-    # -j randomly hangs.
-    script: ruby -C spec/ruby ../mspec/bin/mspec .
+    <<: *spec-on-old-ruby
     after_failure:
       - echo "ruby/spec failed on Ruby 2.7. This is likely because of a missing ruby_version_is guard, please add it. See spec/README.md."