Remove not found url gem

A `bundle install` complaints with:

```
Fetching gem metadata from https://rubygems.org/........
Fetching gem metadata from https://rubygems.org/.
Resolving dependencies....
Your bundle is locked to url (0.3.2), but that version could not be
found in any of the sources listed in your Gemfile. If you haven't
changed sources, that means the author of url (0.3.2) has removed it.
You'll need to update your bundle to a version
other than url (0.3.2) that hasn't been removed in order to install.
```

It looks like that the gem that depends on this one had the same issue
and drop it.

Gemfile.lock

@@ -109,10 +109,9 @@ GEM
       cells (>= 4.1.6, < 5.0.0)
     charlock_holmes (0.7.7)
     childprocess (3.0.0)
-    codecov (0.1.16)
+    codecov (0.2.11)
       json
       simplecov
-      url
     coercible (1.0.0)
       descendants_tracker (~> 0.0.1)
     coffee-rails (5.0.0)
@@ -428,7 +427,7 @@ GEM
       thor (>= 0.14, < 2.0)
     jquery-tmpl-rails (1.1.0)
       rails (>= 3.1.0)
-    json (2.3.0)
+    json (2.3.1)
     jwt (2.2.1)
     kaminari (1.2.0)
       activesupport (>= 4.1.0)
@@ -708,7 +707,6 @@ GEM
       unf_ext
     unf_ext (0.0.7.7)
     unicode-display_width (1.6.1)
-    url (0.3.2)
     valid_email2 (2.3.1)
       activemodel (>= 3.2)
       mail (~> 2.5)
@@ -757,7 +755,7 @@ DEPENDENCIES
   web-console (~> 3.5)
 
 RUBY VERSION
-   ruby 2.6.3p62
+   ruby 2.6.6p146
 
 BUNDLED WITH
    2.1.4