Add Ameba and address code linting issues

src/spectator/example_group.cr

@@ -95,7 +95,7 @@ module Spectator
       offset = index
       # Loop through each child
       # until one is found to contain the index.
-      child = children.each do |child|
+      found = children.each do |child|
         count = child.example_count
         # Example groups consider their range to be [0, example_count).
         # Each child is offset by the total example count of the previous children.
@@ -114,7 +114,7 @@ module Spectator
       # Otherwise, the indexer repeats the process for the next child.
       # It should be impossible to get nil here,
       # provided the bounds check and example counts are correct.
-      child.not_nil![offset]
+      found.not_nil![offset]
     end
 
     # Checks whether all examples in the group have been run.

src/spectator/formatting/human_time.cr

@@ -35,7 +35,7 @@ module Spectator::Formatting
 
       days = hours / 24
       hours %= 24
-      return sprintf("%i days %i:%02i:%02i", days, hours, minutes, int_seconds)
+      sprintf("%i days %i:%02i:%02i", days, hours, minutes, int_seconds)
     end
   end
 end

src/spectator/matchers/array_matcher.cr

@@ -11,8 +11,8 @@ module Spectator::Matchers
       values = ExpectedActual.new(expected, label, actual, partial.label)
       if values.expected.size == values.actual.size
         index = 0
-        values.expected.zip(values.actual) do |expected, actual|
-          return ContentMatchData.new(index, values) unless expected == actual
+        values.expected.zip(values.actual) do |expected, element|
+          return ContentMatchData.new(index, values) unless expected == element
           index += 1
         end
         IdenticalMatchData.new(values)