Add task to install mjml and compile templates for tests

.gitignore

@@ -19,6 +19,7 @@ test/tmp
 test/version_tmp
 tmp
 .byebug_history
+spec/fixtures/*.html
 
 # YARD artifacts
 .yardoc

.travis.yml

@@ -13,6 +13,6 @@ notifications:
   email: false
 
 before_script:
-  - nvm install 6.5
-  - nvm use 6.5
-  - npm install
+  - nvm install node
+  - nvm use node
+  - rake prepare

Rakefile

@@ -8,3 +8,10 @@ Rake::TestTask.new do |t|
 end
 
 task default: :test
+
+# Prepare env for tests
+task :prepare do
+  system 'npm install -g mjml@^2.3.3'
+  template_path = "#{Dir.pwd}/spec/fixtures/hello"
+  system "mjml #{template_path}.mjml -o #{template_path}.html"
+end

lib/mjml/parser.rb

@@ -44,7 +44,7 @@ def mjml_bin
     end
 
     def mjml_version
-      ver = `#{mjml_bin} -V`.strip
+      ver, _status = Open3.capture2(mjml_bin, '-V')
       (ver =~ VERSION_REGEX).nil? ? nil : ver
     end
   end