Fix configuration list defining to override instead of merge

When setting a list value in a custom configuration, `scss-lint` would
merge the value instead of overriding it.

This makes it impossible to remove unwanted values from lists in the
default configuration.

Admittedly, it's pretty surprising we haven't gotten a bug report about
this until now, given this behavior has existed since the configuration
system was added to `scss-lint`.

CHANGELOG.md

@@ -1,5 +1,10 @@
 # SCSS-Lint Changelog
 
+## master (unreleased)
+
+* Change configuration loading behavior so that defining lists in a custom
+  configuration will completely override the old list instead of adding to it
+
 ## 0.37.0
 
 * Rename `BEM` option on `SelectorFormat` to `strict_BEM` to emphasize that

lib/scss_lint/config.rb

@@ -154,8 +154,6 @@ def load_file_contents(file)
       def smart_merge(parent, child)
         parent.merge(child) do |_key, old, new|
           case old
-          when Array
-            old + new
           when Hash
             smart_merge(old, new)
           else

spec/scss_lint/config_spec.rb

@@ -46,6 +46,7 @@ class FakeLinter2 < SCSSLint::Linter; end
     linters:
       FakeConfigLinter:
         enabled: true
+        list: [1, 2, 3]
       OtherFakeConfigLinter:
         enabled: false
     FILE
@@ -104,6 +105,18 @@ class FakeLinter2 < SCSSLint::Linter; end
       end
     end
 
+    context 'with a config file setting a list value different from the default' do
+      let(:config_file) { <<-FILE }
+      linters:
+        FakeConfigLinter:
+          list: [4, 5, 6]
+      FILE
+
+      it 'overrides the default value with the new value' do
+        subject.options['linters']['FakeConfigLinter']['list'].should == [4, 5, 6]
+      end
+    end
+
     context 'when a wildcard is used for a namespaced linter' do
       let(:default_file) { <<-FILE }
       linters: