fix some incorrect symbols before executing command

Signed-off-by: lixiaobing10051267 <li.xiaobing1@zte.com.cn>

docs/reference/commandline/attach.md

@@ -119,7 +119,7 @@ process is returned by the `docker attach` command to its caller too:
     $ docker run --name test -d -it debian
     275c44472aebd77c926d4527885bb09f2f6db21d878c75f0a1c212c03d3bcfab
     $ docker attach test
-    $$ exit 13
+    root@f38c87f2a42d:/# exit 13
     exit
     $ echo $?
     13

docs/reference/commandline/run.md

@@ -546,7 +546,7 @@ more `--add-host` flags. This example adds a static address for a host named
 `docker`:
 
     $ docker run --add-host=docker:10.180.0.1 --rm -it debian
-    $$ ping docker
+    root@f38c87f2a42d:/# ping docker
     PING docker (10.180.0.1): 48 data bytes
     56 bytes from 10.180.0.1: icmp_seq=0 ttl=254 time=7.600 ms
     56 bytes from 10.180.0.1: icmp_seq=1 ttl=254 time=30.705 ms