Allow checking both versions of diff-lcs

Author: JonRowe

.travis.yml

@@ -33,11 +33,13 @@ rvm:
   - jruby-head
   - jruby-1.7
 env:
-  - JRUBY_OPTS='--dev'
+  - JRUBY_OPTS='--dev' DIFF_LCS_VERSION="~> 1.4"
 matrix:
   include:
     - rvm: jruby-1.7
       env: JRUBY_OPTS='--dev --1.8'
+    - rvm: 2.7.1
+      env: DIFF_LCS_VERSION="~> 1.3.0"
   allow_failures:
     - rvm: jruby-head
     - rvm: ruby-head

Gemfile

@@ -21,6 +21,8 @@ else
   gem 'rake', '>= 12.3.3'
 end
 
+gem 'diff-lcs', ENV.fetch('DIFF_LCS_VERSION', '~> 1.4')
+
 if RUBY_VERSION < '2.2.0' && !!(RbConfig::CONFIG['host_os'] =~ /cygwin|mswin|mingw|bccwin|wince|emx/)
   gem "childprocess", "< 1.0.0"
 elsif RUBY_VERSION < '2.3.0'