Update json gem; remove sdoc gem

This fixes the JSON deprecation warning. The sdoc gem wasn't needed,
and it was pulling in psych v5, which wouldn't install (due to a breaking
major version update?).

Gemfile

@@ -15,7 +15,6 @@ gem 'sass-rails', '~> 5.0'
 gem 'underscore-rails'
 
 gem 'jbuilder', '~> 2.7'
-gem 'sdoc', '~> 2.6.1', group: :doc
 gem "highcharts-rails"
 gem 'rails4-autocomplete'
 

Gemfile.lock

@@ -168,8 +168,6 @@ GEM
     parser (2.7.2.0)
       ast (~> 2.4.1)
     powerpack (0.1.3)
-    psych (5.1.0)
-      stringio
     public_suffix (4.0.7)
     puma (5.6.4)
       nio4r (~> 2.0)
@@ -214,8 +212,6 @@ GEM
     rb-fsevent (0.11.1)
     rb-inotify (0.10.1)
       ffi (~> 1.0)
-    rdoc (6.5.0)
-      psych (>= 4.0.0)
     responders (3.0.1)
       actionpack (>= 5.0)
       railties (>= 5.0)
@@ -263,8 +259,6 @@ GEM
       sprockets (>= 2.8, < 4.0)
       sprockets-rails (>= 2.0, < 4.0)
       tilt (>= 1.1, < 3)
-    sdoc (2.6.1)
-      rdoc (>= 5.0)
     sexp_processor (4.16.1)
     spring (4.0.0)
     sprockets (3.7.2)
@@ -274,7 +268,6 @@ GEM
       actionpack (>= 5.2)
       activesupport (>= 5.2)
       sprockets (>= 3.0.0)
-    stringio (3.0.5)
     sys-uptime (0.7.5)
       ffi (~> 1.1)
     temple (0.8.2)
@@ -347,7 +340,6 @@ DEPENDENCIES
   rubocop (~> 0.52.1)
   rubyzip (~> 1.3.0)
   sass-rails (~> 5.0)
-  sdoc (~> 2.6.1)
   spring
   sys-uptime
   timecop
@@ -359,4 +351,4 @@ DEPENDENCIES
   whenever (~> 0.9.7)
 
 BUNDLED WITH
-   2.3.26
+   2.4.7