Update gems

I updated some of these gems for a different project, and
suddenly `rake build` was giving very different output
compared to the current gh-pages. This commit makes sure
everyone updating gh-pages is using reasonably similar
versions, so we avoid spurious diffs.

docs/Gemfile

@@ -4,3 +4,4 @@ gem "rake"
 gem "bonsai"
 gem "maruku"
 gem "ronn"
+gem "mustache", "<1.0" # to support ruby <2.0

docs/Gemfile.lock

@@ -1,15 +1,14 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    POpen4 (0.1.4)
-      Platform (>= 0.4.0)
-      open4
-    Platform (0.4.0)
-    activesupport (3.2.12)
-      i18n (~> 0.6)
-      multi_json (~> 1.0)
-    addressable (2.3.4)
-    bonsai (1.4.8)
+    activesupport (4.2.3)
+      i18n (~> 0.7)
+      json (~> 1.7, >= 1.7.7)
+      minitest (~> 5.1)
+      thread_safe (~> 0.3, >= 0.3.4)
+      tzinfo (~> 1.1)
+    addressable (2.3.8)
+    bonsai (1.4.9)
       activesupport (>= 3.0.3)
       builder (>= 3.0.0)
       i18n (>= 0.5.0)
@@ -22,36 +21,36 @@ GEM
       tilt (>= 1.3)
       watch (>= 0.1.0)
       yui-compressor
-    builder (3.2.0)
+    builder (3.2.2)
     hpricot (0.8.6)
-    i18n (0.6.4)
-    launchy (2.3.0)
+    i18n (0.7.0)
+    json (1.8.3)
+    launchy (2.4.3)
       addressable (~> 2.3)
-    liquid (2.5.0)
-    maruku (0.6.1)
-      syntax (>= 1.0.0)
-    multi_json (1.7.3)
-    mustache (0.99.4)
-    open4 (1.3.0)
-    rack (1.5.2)
-    rack-protection (1.5.0)
+    liquid (3.0.6)
+    maruku (0.7.2)
+    minitest (5.8.0)
+    mustache (0.99.8)
+    rack (1.6.4)
+    rack-protection (1.5.3)
       rack
-    rake (10.0.3)
-    rdiscount (2.0.7.2)
+    rake (10.4.2)
+    rdiscount (2.1.8)
     ronn (0.7.3)
       hpricot (>= 0.8.2)
       mustache (>= 0.7.0)
       rdiscount (>= 1.5.8)
-    sass (3.2.8)
-    sinatra (1.4.2)
-      rack (~> 1.5, >= 1.5.2)
+    sass (3.4.16)
+    sinatra (1.4.6)
+      rack (~> 1.4)
       rack-protection (~> 1.4)
-      tilt (~> 1.3, >= 1.3.4)
-    syntax (1.0.0)
-    tilt (1.4.0)
+      tilt (>= 1.3, < 3)
+    thread_safe (0.3.5)
+    tilt (2.0.1)
+    tzinfo (1.2.2)
+      thread_safe (~> 0.1)
     watch (0.1.0)
-    yui-compressor (0.9.6)
-      POpen4 (>= 0.1.4)
+    yui-compressor (0.12.0)
 
 PLATFORMS
   ruby
@@ -59,5 +58,6 @@ PLATFORMS
 DEPENDENCIES
   bonsai
   maruku
+  mustache (< 1.0)
   rake
   ronn