Update devDependencies, gems and lots of cleanup/build fixes.

* switch to grunt-postcss and autoprefixer directly; this is the recommended way.
* uglify: specify `ie8` for compatibility
* specify `cascade:false` for autoprefixer
* specify `ieCompat` for less
* drop grunt-contrib-compress since it doesn't work with Node.js 10.x
* remove grunt-contrib-htmlmin to match the v4 docs
* clean up Gruntfile.js
* clean up .travis.yml and backport changes from v4
* build ie10-viewport-bug-workaround.less since it's used in examples
* move shrinkwrap to root
* bs-commonjs-generator.js: Use `path.posix`
* remove .hound.yml
* remove references to no longer used PR bots
* backport and adapt the sri generation script from v4

Gemfile.lock

@@ -1,37 +1,57 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    addressable (2.4.0)
-    colorator (0.1)
-    ffi (1.9.18)
-    ffi (1.9.18-x64-mingw32)
-    jekyll (3.1.6)
-      colorator (~> 0.1)
+    addressable (2.5.2)
+      public_suffix (>= 2.0.2, < 4.0)
+    colorator (1.1.0)
+    concurrent-ruby (1.1.3)
+    em-websocket (0.5.1)
+      eventmachine (>= 0.12.9)
+      http_parser.rb (~> 0.6.0)
+    eventmachine (1.2.7)
+    eventmachine (1.2.7-x64-mingw32)
+    ffi (1.9.25)
+    ffi (1.9.25-x64-mingw32)
+    forwardable-extended (2.6.0)
+    http_parser.rb (0.6.0)
+    i18n (0.9.5)
+      concurrent-ruby (~> 1.0)
+    jekyll (3.8.5)
+      addressable (~> 2.4)
+      colorator (~> 1.0)
+      em-websocket (~> 0.5)
+      i18n (~> 0.7)
       jekyll-sass-converter (~> 1.0)
-      jekyll-watch (~> 1.1)
-      kramdown (~> 1.3)
-      liquid (~> 3.0)
+      jekyll-watch (~> 2.0)
+      kramdown (~> 1.14)
+      liquid (~> 4.0)
       mercenary (~> 0.3.3)
-      rouge (~> 1.7)
+      pathutil (~> 0.9)
+      rouge (>= 1.7, < 4)
       safe_yaml (~> 1.0)
-    jekyll-sass-converter (1.5.0)
+    jekyll-sass-converter (1.5.2)
       sass (~> 3.4)
-    jekyll-sitemap (0.11.0)
-      addressable (~> 2.4.0)
-    jekyll-watch (1.5.0)
-      listen (~> 3.0, < 3.1)
-    kramdown (1.14.0)
-    liquid (3.0.6)
-    listen (3.0.8)
+    jekyll-sitemap (1.2.0)
+      jekyll (~> 3.3)
+    jekyll-watch (2.1.2)
+      listen (~> 3.0)
+    kramdown (1.17.0)
+    liquid (4.0.1)
+    listen (3.1.5)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
+      ruby_dep (~> 1.2)
     mercenary (0.3.6)
-    rb-fsevent (0.10.2)
+    pathutil (0.16.2)
+      forwardable-extended (~> 2.6)
+    public_suffix (3.0.3)
+    rb-fsevent (0.10.3)
     rb-inotify (0.9.10)
       ffi (>= 0.5.0, < 2)
-    rouge (1.11.1)
+    rouge (3.3.0)
+    ruby_dep (1.5.0)
     safe_yaml (1.0.4)
-    sass (3.5.1)
+    sass (3.7.2)
       sass-listen (~> 4.0.0)
     sass-listen (4.0.0)
       rb-fsevent (~> 0.9, >= 0.9.4)
@@ -42,8 +62,8 @@ PLATFORMS
   x64-mingw32
 
 DEPENDENCIES
-  jekyll (~> 3.1.2)
-  jekyll-sitemap (~> 0.11.0)
+  jekyll (~> 3.8.5)
+  jekyll-sitemap (~> 1.2.0)
 
 BUNDLED WITH
-   1.15.3
+   1.17.2