minor fix keywords delimit (#739)
### Prerequisites
- [x] This pull request fixes a very minor bug.
### Description
Some very minor fix in head meta keywords


### Fixed

| | |
| | | {{ with .Site.Params.author }} |
| | | <meta name="author" content="{{ . }}">{{ end }} |
| | | <meta name="description" content="{{ .Description | default (.Summary | default .Site.Params.description ) }}"> |
| | | <meta name="keywords" content="{{ (delimit .Keywords " ,") | default .Site.Params.keywords }}"> |
| | | <meta name="keywords" content="{{ (delimit .Keywords ", ") | default .Site.Params.keywords }}"> |
| | | |
| | | {{ template "_internal/twitter_cards.html" . }} |
| | | {{ template "_internal/opengraph.html" . }} |