Revert to Hugo v0.19

v0.20 is not working properly with the current site.

Author: ericp1337

.travis.yml

@@ -8,7 +8,7 @@ env:
     - PHP_VERSION=56
     - PHP_VERSION=70
     - PHP_VERSION=71
-    - HUGO_VERSION=0.20
+    - HUGO_VERSION=0.19
 
 script: ./_scripts/travis-build.sh