use different libcurl dependency?

based on info in https://github.com/gjtorikian/html-proofer/wiki/Using-HTMLProofer-From-Ruby-and-Travis
....

Author: jbjonesjr

.travis.yml

@@ -2,10 +2,21 @@ language: ruby
 script: "./script/cibuild"
 notifications:
   email: false
+
+env:
+  global:
+  - NOKOGIRI_USE_SYSTEM_LIBRARIES=true # speeds up installation of html-proofer
+
+addons:
+  apt:
+    packages:
+    - libcurl4-openssl-dev # required to avoid SSL errors
+
 branches:
   only:
     - gh-pages
     - /.*/
+
 before_install:
 - openssl version
 - openssl ciphers -v