Update install-machine.md (docker#5900)

The installation method is optimized and the installation process is more concise

Author: sjkcdpc

machine/install-machine.md

@@ -32,8 +32,7 @@ on GitHub.
 
     ```console
     $ curl -L https://github.com/docker/machine/releases/download/v{{site.machine_version}}/docker-machine-`uname -s`-`uname -m` >/tmp/docker-machine && \
-    chmod +x /tmp/docker-machine && \
-    sudo cp /tmp/docker-machine /usr/local/bin/docker-machine
+    sudo install /tmp/docker-machine /usr/local/bin/docker-machine
     ```
 
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