fix incorrect docstring (#280)

* fix incorrect docstring

* Update schema_components.py

Co-authored-by: Niels Bantilan <niels.bantilan@gmail.com>

pandera/schema_components.py

@@ -41,8 +41,8 @@ def __init__(
             http://pandas.pydata.org/pandas-docs/stable/basics.html#dtypes
         :param checks: checks to verify validity of the column
         :param nullable: Whether or not column can contain null values.
-        :param allow_duplicates: Whether or not to coerce the column to the
-            specified pandas_dtype before validation
+        :param allow_duplicates: Whether or not column can contain duplicate
+            values.
         :param coerce: If True, when schema.validate is called the column will
             be coerced into the specified dtype.
         :param required: Whether or not column is allowed to be missing