Add spec for \s matching newline

spec/propane/lexer/dfa_spec.rb

@@ -187,6 +187,13 @@ EOF
     ]
     expect(run(<<EOF, "$&*")).to eq expected
 token t /[^%\\W]+/;
+EOF
+  end
+
+  it "\\s matches a newline" do
+    expected = [["s", "\n"]]
+    expect(run(<<EOF, "\n")).to eq expected
+token s /\\s/;
 EOF
   end
 end