Add and apply Style/BlockDelimiters rubocop rule

We were already using it most of the time, but there were a few places
were we used brackets for multiline blocks.

.rubocop_basic.yml

@@ -41,6 +41,9 @@ Layout/EmptyLines:
 Layout/EndOfLine:
   EnforcedStyle: lf
 
+Layout/MultilineBlockLayout:
+  Enabled: true
+
 Layout/SpaceAfterColon:
   Enabled: true
 
@@ -229,6 +232,9 @@ RSpec/ScatteredSetup:
 RSpec/VoidExpect:
   Enabled: true
 
+Style/BlockDelimiters:
+  Enabled: true
+
 Style/PercentLiteralDelimiters:
   Enabled: true