[Security] Bump rest-client from 1.6.7 to 2.1.0

Bumps [rest-client](https://github.com/rest-client/rest-client) from 1.6.7 to 2.1.0. **This update includes security fixes.**
- [Release notes](https://github.com/rest-client/rest-client/releases)
- [Changelog](https://github.com/rest-client/rest-client/blob/master/history.md)
- [Commits](rest-client/rest-client@v1.6.7...v2.1.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Gemfile.lock

@@ -17,16 +17,27 @@ GEM
       simplecov (>= 0.7)
       term-ansicolor
       thor
+    domain_name (0.5.20190701)
+      unf (>= 0.0.5, < 1.0.0)
+    http-accept (1.7.0)
+    http-cookie (1.0.3)
+      domain_name (~> 0.5)
     json (2.2.0)
-    mime-types (1.25)
+    mime-types (3.2.2)
+      mime-types-data (~> 3.2015)
+    mime-types-data (3.2019.0331)
     mini_portile (0.5.1)
     minitest (5.0.8)
     multi_json (1.8.0)
+    netrc (0.11.0)
     nokogiri (1.6.0)
       mini_portile (~> 0.5.0)
     rake (12.3.3)
-    rest-client (1.6.7)
-      mime-types (>= 1.16)
+    rest-client (2.1.0)
+      http-accept (>= 1.7.0, < 2.0)
+      http-cookie (>= 1.0.2, < 2.0)
+      mime-types (>= 1.16, < 4.0)
+      netrc (~> 0.8)
     simplecov (0.7.1)
       multi_json (~> 1.0)
       simplecov-html (~> 0.7.1)
@@ -35,6 +46,9 @@ GEM
       tins (~> 0.8)
     thor (0.20.3)
     tins (0.11.0)
+    unf (0.1.4)
+      unf_ext
+    unf_ext (0.0.7.6)
 
 PLATFORMS
   ruby