fix: grep warnings during generating usage documentation

to prevent `grep: warning: stray \ before -` and accidental non-zero return
codes

govc/usage.sh

@@ -49,7 +49,7 @@ printf "%s\n\`\`\`\n\n" "${common_opts}"
 
 cmds=($(govc -h | sed '1,/^Available commands:$/d'))
 
-opts=($(cut -s -d= -f1 <<<"$common_opts" | xargs -n1 | sed -e 's/^/\\/'))
+opts=($(cut -s -d= -f1 <<<"$common_opts" | xargs -n1))
 filter=$(printf "|%s=" "${opts[@]}")
 
 printf "<details><summary>Contents</summary>\n\n"
@@ -61,6 +61,6 @@ printf "\n</details>\n\n"
 for cmd in "${cmds[@]}" ; do
     printf "## %s\n\n" "$cmd"
     printf "\`\`\`\n"
-    govc "$cmd" -h | egrep -v "${filter:1}"
+    govc "$cmd" -h | grep -E -v -- "${filter:1}"
     printf "\`\`\`\n\n"
 done