Explicitly set the TRAVIS env in Guardfile

Author: just3ws

Guardfile

@@ -1,5 +1,5 @@
 group :rspec, halt_on_fail: true do
-  guard :rspec, failed_mode: :keep, all_on_start: false, all_after_pass: false, cmd: 'bin/rspec spec/' do
+  guard :rspec, failed_mode: :keep, all_on_start: false, all_after_pass: false, cmd: 'TRAVIS=true bundle exec rspec spec/' do
     watch(%r{^spec/.+_spec\.rb$})
     watch(%r{^lib/(.+)\.rb$}) { |m| "spec/lib/#{m[1]}_spec.rb" }
     watch('spec/spec_helper.rb') { "spec" }