[company-go]: Passes a -source flag to gocode by default

I also noticed that the forked gocode does not support `csv-with-package`, and so I changed this at the same time. I am increasingly unsure if this change should be merged, or if the version in MELPA should be repointed to the forked company-go.

Fixes nsf#529

emacs-company/company-go.el

@@ -71,7 +71,8 @@ symbol is preceded by a \".\", ignoring `company-minimum-prefix-length'."
 (defun company-go--invoke-autocomplete ()
  (let ((code-buffer (current-buffer))
  (gocode-args (append company-go-gocode-args
- (list "-f=csv-with-package"
+ (list "-source"
+ "-f=csv"
  "autocomplete"
  (or (buffer-file-name) "")
  (concat "c" (int-to-string (- (point) 1)))))))