Update links in _repos to point to monorepo trees

Author: JonRowe

source/_repos.html.slim

@@ -4,21 +4,17 @@ ul
     = link_to 'https://github.com/rspec/rspec-rails', 'https://github.com/rspec/rspec-rails'
   li
     | For bugs with rspec-core: 
-    = link_to 'https://github.com/rspec/rspec-core', 'https://github.com/rspec/rspec-core'
+    = link_to 'https://github.com/rspec/rspec/tree/main/rspec-core', 'https://github.com/rspec/rspec/tree/main/rspec-core'
     |  (runner, configuration, etc)
   li
     | For bugs with rspec-mocks: 
-    = link_to 'https://github.com/rspec/rspec-mocks', 'https://github.com/rspec/rspec-mocks'
+    = link_to 'https://github.com/rspec/rspec/tree/main/rspec-mocks', 'https://github.com/rspec/rspec/tree/main/rspec-mocks'
     |  (doubles, spies, etc)
   li
     | For bugs with rspec-expectations: 
-    = link_to 'https://github.com/rspec/rspec-expectations', 'https://github.com/rspec/rspec-expectations'
+    = link_to 'https://github.com/rspec/rspec/tree/main/rspec-expectations', 'https://github.com/rspec/rspec/tree/main/rspec-expectations'
     |  (matchers)
   li
     | For bugs with rspec-support: 
-    = link_to 'https://github.com/rspec/rspec-support', 'https://github.com/rspec/rspec-support'
+    = link_to 'https://github.com/rspec/rspec/tree/main/rspec-support', 'https://github.com/rspec/rspec/tree/main/rspec-support'
     |  (string encoding, failed expectation diffing, Ruby feature detection, etc)
-  li
-    | For bugs with rspec-dev: 
-    = link_to 'https://github.com/rspec/rspec-dev', 'https://github.com/rspec/rspec-dev'
-    |  (tools for developing rspec)