fix erroneous indent and add abstractmethod to HMACBackend
diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index 45fbaf0..5b6cd64 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -141,8 +141,8 @@
Create a
:class:`~cryptogrpahy.hazmat.primitives.interfaces.HashContext` that
- uses the specified ``algorithm`` to calculate a hash-based message
- authentication code.
+ uses the specified ``algorithm`` to calculate a hash-based message
+ authentication code.
:param algorithm: An instance of a
:class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`