fix security vulnerabilities (daattali#423)

Author: npes87184

Gemfile.lock

@@ -15,7 +15,7 @@ GEM
     colorator (1.1.0)
     concurrent-ruby (1.0.5)
     ethon (0.11.0)
-      ffi (>= 1.3.0)
+      ffi (>= 1.9.24)
     execjs (2.7.0)
     faraday (0.13.1)
       multipart-post (>= 1.2, < 3)
@@ -26,7 +26,7 @@ GEM
     github-pages (163)
       activesupport (= 4.2.9)
       github-pages-health-check (= 1.3.5)
-      jekyll (= 3.5.2)
+      jekyll (= 3.6.3)
       jekyll-avatar (= 0.5.0)
       jekyll-coffeescript (= 1.0.2)
       jekyll-default-layout (= 0.1.4)