docs: add gzip arg to BuildApiMixin (#2929)

Signed-off-by: Saurav Maheshkar <sauravvmaheshkar@gmail.com>

docker/api/build.py

@@ -76,6 +76,7 @@ def build(self, path=None, tag=None, quiet=False, fileobj=None,
             forcerm (bool): Always remove intermediate containers, even after
                 unsuccessful builds
             dockerfile (str): path within the build context to the Dockerfile
+            gzip (bool): If set to ``True``, gzip compression/encoding is used
             buildargs (dict): A dictionary of build arguments
             container_limits (dict): A dictionary of limits applied to each
                 container created by the build process. Valid keys: