style: unify indentation in RuboCop configuration

Some elements already used two-space indentation and we also prefer two
spaces in our Ruby code.

Closes #306.

Signed-off-by: Martin Afanasjew <martin@afanasjew.de>

Library/.rubocop.yml

@@ -5,111 +5,111 @@ AllCops:
 
 # 1.8-style hash keys
 Style/HashSyntax:
-    EnforcedStyle: hash_rockets
+  EnforcedStyle: hash_rockets
 
 # ruby style guide favorite
 Style/StringLiterals:
-    EnforcedStyle: double_quotes
+  EnforcedStyle: double_quotes
 
 # consistency with above
 Style/StringLiteralsInInterpolation:
-    EnforcedStyle: double_quotes
+  EnforcedStyle: double_quotes
 
 # percent-x is allowed for multiline
 Style/CommandLiteral:
-    EnforcedStyle: mixed
+  EnforcedStyle: mixed
 
 # paths abound, easy escape
 Style/RegexpLiteral:
-    EnforcedStyle: slashes
+  EnforcedStyle: slashes
 
 # our current conditional style is established, clear and
 # requiring users to change that now would be confusing.
 Style/ConditionalAssignment:
-    Enabled: false
+  Enabled: false
 
 # no metrics for formulas
 Metrics/AbcSize:
-    Enabled: false
+  Enabled: false
 Metrics/CyclomaticComplexity:
-    Enabled: false
+  Enabled: false
 Metrics/MethodLength:
-    Enabled: false
+  Enabled: false
 Metrics/ClassLength:
-    Enabled: false
+  Enabled: false
 Metrics/PerceivedComplexity:
-    Enabled: false
+  Enabled: false
 
 # we often need very long lines
 Metrics/LineLength:
-    Enabled: false
+  Enabled: false
 
 # formulas have no mandatory doc
 Style/Documentation:
-    Enabled: false
+  Enabled: false
 
 # favor parens-less DSL-style arguments
 Lint/AmbiguousOperator:
-    Enabled: false
+  Enabled: false
 Lint/AmbiguousRegexpLiteral:
-    Enabled: false
+  Enabled: false
 Lint/AssignmentInCondition:
-    Enabled: false
+  Enabled: false
 Lint/ParenthesesAsGroupedExpression:
-    Enabled: false
+  Enabled: false
 
 # compact style
 Style/EmptyLineBetweenDefs:
-    AllowAdjacentOneLineDefs: true
+  AllowAdjacentOneLineDefs: true
 
 # port numbers and such tech stuff
 Style/NumericLiterals:
-    Enabled: false
+  Enabled: false
 
 # consistency and readability when faced with string interpolation
 Style/PercentLiteralDelimiters:
-    PreferredDelimiters:
-        '%':  '()'
-        '%i': '()'
-        '%q': '()'
-        '%Q': '()'
-        '%r': '{}'
-        '%s': '()'
-        '%w': '[]'
-        '%W': '[]'
-        '%x': '()'
+  PreferredDelimiters:
+    '%':  '()'
+    '%i': '()'
+    '%q': '()'
+    '%Q': '()'
+    '%r': '{}'
+    '%s': '()'
+    '%w': '[]'
+    '%W': '[]'
+    '%x': '()'
 
 # conflicts with DSL-style path concatenation with `/`
 Style/SpaceAroundOperators:
-    Enabled: false
+  Enabled: false
 
 # not a problem for typical shell users
 Style/SpecialGlobalVars:
-    Enabled: false
+  Enabled: false
 
 # `system` is a special case and aligns on second argument
 Style/AlignParameters:
-    Enabled: false
+  Enabled: false
 
 # counterproductive in formulas, notably within the install method
 Style/GuardClause:
-    Enabled: false
+  Enabled: false
 Style/IfUnlessModifier:
-    Enabled: false
+  Enabled: false
 
 # dashes in filenames are typical
 # TODO: enforce when rubocop has fixed this
 # https://github.com/bbatsov/rubocop/issues/1545
 Style/FileName:
-    Enabled: false
+  Enabled: false
 
 # no percent word array, being friendly to non-ruby users
 # TODO: enforce when rubocop has fixed this
 # https://github.com/bbatsov/rubocop/issues/1543
 Style/WordArray:
-    Enabled: false
+  Enabled: false
 Style/UnneededCapitalW:
-    Enabled: false
+  Enabled: false
 
 # we use raise, not fail
 Style/SignalException: