Properly support Unicode Strings (#3)

* Properly support unicode strings

```
iex(47)> "✔︎" |> String.replace(~r/[\p{P}\p{S}]/, " ") |> String.valid?
false
iex(48)> "✔︎" |> String.replace(~r/[\p{P}\p{S}]/u, " ") |> String.valid?
true
```

* add a test case for unicode strings

Co-authored-by: Ryan Johnson <ryan@grain.com>

lib/fuzzy_compare/preprocessor.ex

@@ -11,7 +11,7 @@ defmodule FuzzyCompare.Preprocessor do
   alias FuzzyCompare.Preprocessed
 
   # Replaces all punctuation
-  @regex ~r/[\p{P}\p{S}]/
+  @regex ~r/[\p{P}\p{S}]/u
 
   @spec process(binary(), binary()) :: {Preprocessed.t(), Preprocessed.t()}
   def process(left, right) when is_binary(left) and is_binary(right) do

test/preprocessor_test.exs

@@ -0,0 +1,10 @@
+defmodule PreprocessorTest do
+  use ExUnit.Case
+
+  @subject FuzzyCompare.Preprocessor
+
+  test "when replacing whitespace and punctuation in unicode strings the string remains a valid unicode string" do
+    result = @subject.process("✔︎")
+    assert String.valid?(result.string) == true
+  end
+end