Ensure dashes and underscores are permitted in key names

The validation added #36 is too strict, it doesn't allow underscores,
hyphens, and spaces. These are supposed to be permissible as long as
they don't come at the beginning or end.

This makes the following changes to the ReGex:
- Add " ", "_", and "-" to the allowed middle of word characters
- Change "\u10FFFFA" to "\u10FF". This caused a warning from Ruby
  because it doesn't understand utf16 codes and the extra F and A
  characters were interpreted as literals.

Fixes #37

Author: jonmast

lib/jsonapi/include_directive.rb

@@ -81,7 +81,7 @@ def valid?(key)
 
     def valid_json_key_name_regex
       # https://jsonapi.org/format/#document-member-names
-      /^(?![\s\-_])[\u0080-\u10FFFFA-Za-z0-9*]+(?<![\s\-_])$/
+      /^(?![\s\-_])[\u0080-\u10FFA-Za-z0-9* _-]+(?<![\s\-_])$/
     end
   end
 end

spec/include_directive_spec.rb

@@ -31,12 +31,19 @@
     end
   end
 
-  context 'not raises InvalidKey' do
+  context 'does not raise InvalidKey' do
     ["\u0080", "B", "t", "5", "\u0100", "\u10FFFAA"].each do |char|
-      it "when provided characher '#{char}'" do
+      it "when provided character '#{char}'" do
         expect(JSONAPI::IncludeDirective.new(char).key?(char)).to be true
       end
     end
+
+    [' ', '_', '-'].each do |char|
+      it "when '#{char}' is not at beginning or end" do
+        key = "valid#{char}valid"
+        expect(JSONAPI::IncludeDirective.new(key).key?(key)).to be true
+      end
+    end
   end
 end