fix(vet): query.cmd was always set to ":" (#2525)

Also update comment on Query message to list values without :

Author: thokra-nav

docs/howto/vet.md

@@ -29,7 +29,7 @@ message Query
   string sql = 1;
   // Name of the query
   string name = 2; 
-  // One of :many, :one, :exec, etc.
+  // One of "many", "one", "exec", etc.
   string cmd = 3;
   // Query parameters, if any
   repeated Parameter params = 4;

internal/cmd/vet.go

@@ -446,7 +446,7 @@ func vetQuery(q *plugin.Query) *vet.Query {
 	return &vet.Query{
 		Sql:    q.Text,
 		Name:   q.Name,
-		Cmd:    strings.TrimPrefix(":", q.Cmd),
+		Cmd:    strings.TrimPrefix(q.Cmd, ":"),
 		Params: params,
 	}
 }

internal/endtoend/testdata/vet_failures/stderr.txt

@@ -4,3 +4,4 @@ query.sql: CreateAuthor: no-pg: invalid engine: postgresql
 query.sql: CreateAuthor: only-one-param: too many parameters
 query.sql: DeleteAuthor: no-pg: invalid engine: postgresql
 query.sql: DeleteAuthor: no-delete: don't use delete statements
+query.sql: DeleteAuthor: no-exec: don't use exec