Update webmock dev dependency

This is fixing this spec issue:

```
1) VideoInfo::Providers::Youtube with video WVsj2pS-zFY #description
     Failure/Error: Oga.parse_html(open(api_url).read)

     ArgumentError:
       unknown keyword: write_timeout
     # (eval):1:in `initialize'
     # 
./bundle/ruby/2.6.0/gems/webmock-2.3.2/lib/webmock/http_lib_adapters/net_http.rb:136:in 
`start_with_connect_without_finish'
     # 
./bundle/ruby/2.6.0/gems/webmock-2.3.2/lib/webmock/http_lib_adapters/net_http.rb:104:in 
`request'
     # 
./bundle/ruby/2.6.0/gems/webmock-2.3.2/lib/webmock/http_lib_adapters/net_http.rb:123:in 
`start_without_connect'
     # 
./bundle/ruby/2.6.0/gems/webmock-2.3.2/lib/webmock/http_lib_adapters/net_http.rb:150:in 
`start'
     # ./lib/video_info/providers/youtube_scraper.rb:94:in 
`_set_data_from_api_impl'
     # ./lib/video_info/provider.rb:83:in `_set_data_from_api'
     # ./lib/video_info/provider.rb:32:in `data'
     # ./lib/video_info/providers/youtube_scraper.rb:9:in `available?'
     # ./lib/video_info/providers/youtube_scraper.rb:66:in 
`meta_node_value'
     # ./lib/video_info/providers/youtube_scraper.rb:32:in `description'
     # ./spec/lib/video_info/providers/youtube_scraper_spec.rb:8:in 
`block (4 levels) in <top (required)>'
     # ./spec/lib/video_info/providers/youtube_scraper_spec.rb:9:in 
`block (4 levels) in <top (required)>'
```

video_info.gemspec

@@ -30,5 +30,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rspec-its', '~> 1.2'
   s.add_development_dependency 'rubocop', '~> 0.37'
   s.add_development_dependency 'vcr', '~> 3.0.3'
-  s.add_development_dependency 'webmock', '~> 2.3.2'
+  s.add_development_dependency 'webmock', '~> 3.7'
 end