docs: fix a typo in docker-build man page

s/Dockefile/Dockerfile

Signed-off-by: Chen Hanxiao <chenhanxiao@cn.fujitsu.com>

docs/man/docker-build.1.md

@@ -59,7 +59,7 @@ as context.
 
 # EXAMPLES
 
-## Building an image using a Dockefile located inside the current directory
+## Building an image using a Dockerfile located inside the current directory
 
 Docker images can be built using the build command and a Dockerfile: