tiny typo fix for min length validator's error string

src/attr/validators.py

@@ -581,7 +581,7 @@ def __call__(self, inst, attr, value):
         """
         if len(value) < self.min_length:
             raise ValueError(
-                "Length of '{name}' must be => {min}: {len}".format(
+                "Length of '{name}' must be >= {min}: {len}".format(
                     name=attr.name, min=self.min_length, len=len(value)
                 )
             )