fix argument error with _small_caps

src/mutators.py

@@ -125,6 +125,7 @@ class SmallCaps(TextMutator):
     def mutate(self, text: str) -> str:
         return "".join(self._small_cap(char) for char in text)
 
+    @staticmethod
     def _small_cap(char: str) -> str:
         if "a" <= char <= "z":
             return chr(ord(char) + 0x1D00 - ord("a"))
@@ -229,4 +230,3 @@ r.register("dbl_chars", DoubleCharacters)
 r.register("backwards_words", BackwardsWords)
 r.register("shakespear", ShakeSpearean)
 # r.register("", )
-