Use inspect on values in to_s

The to_json method calls to_s, which results in incorrect output.

src/spectator/matchers/alternative_match_data_value.cr

@@ -21,7 +21,7 @@ module Spectator::Matchers
 
     # Produces a stringified value.
     def to_s(io)
-      io << value
+      @value.inspect(io)
     end
 
     # Produces a stringified value with additional information.

src/spectator/matchers/generic_match_data_value.cr

@@ -12,7 +12,7 @@ module Spectator::Matchers
 
     # Stringifies the value.
     def to_s(io)
-      io << @value
+      @value.inspect(io)
     end
 
     # Inspects the value.

src/spectator/matchers/negatable_match_data_value.cr

@@ -21,7 +21,7 @@ module Spectator::Matchers
     # The string will be prefixed with "Not" when negated.
     def to_s(io)
       io << "Not " if @negated
-      io << @value
+      @value.inspect(io)
     end
 
     # Produces a stringified value with additional information.

src/spectator/matchers/negatable_prefixed_match_data_value.cr

@@ -26,7 +26,7 @@ module Spectator::Matchers
     def to_s(io)
       io << prefix
       io << ' '
-      io << @value
+      @value.inspect(io)
     end
 
     # Produces a stringified value with additional information.

src/spectator/matchers/prefixed_match_data_value.cr

@@ -14,7 +14,7 @@ module Spectator::Matchers
     def to_s(io)
       io << @prefix
       io << ' '
-      io << @value
+      @value.inspect(io)
     end
 
     # Outputs details of the formatted value with a prefix.