Rubocop: consistent array indentation.

This commit updates the Rubocop configuration to match the code style for
arrays that's used in this project. The Rubocop default must have changed at
some point.

Author: georgebrock

.rubocop.yml

@@ -1,3 +1,8 @@
+Layout/IndentArray:
+  Description: Checks the indentation of the first element in an array literal.
+  Enabled: true
+  EnforcedStyle: consistent
+
 Style/StringLiterals:
   Description: Checks if uses of quotes match the configured preference.
   StyleGuide: https://github.com/bbatsov/ruby-style-guide#consistent-string-literals