updates import statements

Usage:
  gopls [flags] imports [imports-flags] <filename>

Example: update imports statements in a file:

	$ gopls imports -w internal/cmd/check.go

imports-flags:
  -d,-diff
    	display diffs instead of edited file content
  -l,-list
    	display names of edited files
  -preserve
    	with -write, make copies of original files
  -w,-write
    	write edited content to source files
