gopls/internal/cmd: Improve help texts

`gopls check` operates on multiple files, so I made the help text
reflect that fact.

Author: silverwind

gopls/internal/cmd/check.go

@@ -21,8 +21,8 @@ type check struct {
 
 func (c *check) Name() string      { return "check" }
 func (c *check) Parent() string    { return c.app.Name() }
-func (c *check) Usage() string     { return "<filename>" }
-func (c *check) ShortHelp() string { return "show diagnostic results for the specified file" }
+func (c *check) Usage() string     { return "<files>" }
+func (c *check) ShortHelp() string { return "show diagnostic results for the specified files" }
 func (c *check) DetailedHelp(f *flag.FlagSet) {
 	fmt.Fprint(f.Output(), `
 Example: show the diagnostic results of this file:

gopls/internal/cmd/usage/check.hlp

@@ -1,7 +1,7 @@
-show diagnostic results for the specified file
+show diagnostic results for the specified files
 
 Usage:
-  gopls [flags] check <filename>
+  gopls [flags] check <files>
 
 Example: show the diagnostic results of this file:
 

gopls/internal/cmd/usage/usage-v.hlp

@@ -20,7 +20,7 @@ Main
 
 Features            
   call_hierarchy    display selected identifier's call hierarchy
-  check             show diagnostic results for the specified file
+  check             show diagnostic results for the specified files
   codelens          List or execute code lenses for a file
   definition        show declaration of selected identifier
   execute           Execute a gopls custom LSP command

gopls/internal/cmd/usage/usage.hlp

@@ -20,7 +20,7 @@ Main
 
 Features            
   call_hierarchy    display selected identifier's call hierarchy
-  check             show diagnostic results for the specified file
+  check             show diagnostic results for the specified files
   codelens          List or execute code lenses for a file
   definition        show declaration of selected identifier
   execute           Execute a gopls custom LSP command