Add tidy check to travis

.travis.yml

@@ -4,6 +4,7 @@ before_install:
   - sudo apt-get update -qq
   - sudo apt-get install bc
   - sudo apt-get install python-rdflib python-yaml
+  - sudo apt-get install tidy
 #compiler:
 #  - clang
 #  - gcc
@@ -11,5 +12,6 @@ script:
   # Apply TRAVIS=1 to codepolicycheck to make it error out on failures;
   # don't prevent apitest/qecmatest which also do a policy check.
   - TRAVIS=1 make codepolicycheck
+  - make tidy-site
   - make apitest
   - make qecmatest