image/spec: Fix typo in "superseded"

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

image/spec/v1.1.md

@@ -1,7 +1,7 @@
 # Docker Image Specification v1.1.0
 
 This Document described the Docker Image Specification used by Docker Engine
-v1.10.0 and up. It has been supserseeded by Docker Image Specification v1.2.0.
+v1.10.0 and up. It has been superseded by Docker Image Specification v1.2.0.
 
 The Docker Image Specification is the image specification as used by the
 Docker Engine, and was used as foundation of the OCI image specification.

image/spec/v1.md

@@ -1,7 +1,7 @@
 # Docker Image Specification v1.0.0
 
 This Document described the Docker Image Specification used by Docker Engine
-before v1.10.0. It has been supserseeded by Docker Image Specification v1.1.0.
+before v1.10.0. It has been superseded by Docker Image Specification v1.1.0.
 
 The Docker Image Specification is the image specification as used by the
 Docker Engine, and was used as foundation of the OCI image specification.