Make CodeClimate config more strict

There's no point of using Code Climate if most of its checks are
disabled. Now it scores our codebase with an A and reports just 2 code
smells, 64 duplications and 14 other issues. That couldn't farther from
reality. If we care about the architecture and maintainability of our
app, this is a must.

To transition towards enabling all default checks, I started with
scss-lint, duplication and method-complexity. This doesn't mean will
have to fix them all straight away as we'll add the current violations
to the `.rubocop_todo.yml` but it'll point us the parts where we should
focus our efforts.

.codeclimate.yml

@@ -4,7 +4,7 @@ plugins:
     enabled: true
     channel: "rubocop-0-55"
   scss-lint:
-    enabled: false
+    enabled: true
   duplication:
     enabled: true
     exclude_patterns:
@@ -16,9 +16,9 @@ checks:
   complex-logic:
     enabled: true
   file-lines:
-    enabled: false
+    enabled: true
   method-complexity:
-    enabled: false
+    enabled: true
   method-count:
     enabled: false
   method-lines:
@@ -35,3 +35,4 @@ exclude_patterns:
 - "spec/**/*"
 - "vendor/**/*"
 - "app/assets/javascripts/shared/*"
+- "app/assets/javascripts/jquery-migrate-1.0.0.js"