s/which/that/

Which is usually for descriptive clauses in technical writing, while
that is restrictive. Most of the time we are being being restrictive.
diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index 5131ca1..cd64050 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -16,7 +16,7 @@
 
 .. class:: CipherBackend
 
-    A backend which provides methods for using ciphers for encryption
+    A backend that provides methods for using ciphers for encryption
     and decryption.
 
     The following backends implement this interface:
diff --git a/docs/hazmat/backends/multibackend.rst b/docs/hazmat/backends/multibackend.rst
index 95538ac..119b13a 100644
--- a/docs/hazmat/backends/multibackend.rst
+++ b/docs/hazmat/backends/multibackend.rst
@@ -10,7 +10,7 @@
     .. versionadded:: 0.2
 
     This class allows you to combine multiple backends into a single backend
-    which offers the combined features of all of its constituents.
+    that offers the combined features of all of its constituents.
 
     .. code-block:: pycon
 
diff --git a/docs/hazmat/primitives/cryptographic-hashes.rst b/docs/hazmat/primitives/cryptographic-hashes.rst
index 3834737..6c56aca 100644
--- a/docs/hazmat/primitives/cryptographic-hashes.rst
+++ b/docs/hazmat/primitives/cryptographic-hashes.rst
@@ -56,7 +56,7 @@
         :meth:`finalize` and get an intermediate digest value while we continue
         to call :meth:`update` on the original.
 
-        :return: A new instance of :class:`Hash` which can be updated
+        :return: A new instance of :class:`Hash` that can be updated
             and finalized independently of the original instance.
         :raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize`
 
diff --git a/docs/hazmat/primitives/hmac.rst b/docs/hazmat/primitives/hmac.rst
index a21799b..0118be7 100644
--- a/docs/hazmat/primitives/hmac.rst
+++ b/docs/hazmat/primitives/hmac.rst
@@ -67,7 +67,7 @@
         :meth:`finalize` and get an intermediate digest value while we continue
         to call :meth:`update` on the original.
 
-        :return: A new instance of :class:`HMAC` which can be updated
+        :return: A new instance of :class:`HMAC` that can be updated
             and finalized independently of the original instance.
         :raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize`