breaking changes: Open_Graph_meta 設置更改，可配置其它參數

feature: 更新 Facebook sdk 到 v15
improvement: 更新 plugins.yml
Remove: 移除 meta keywords

layout/includes/head.pug

@@ -7,11 +7,6 @@
 
 - var isSubtitle = config.subtitle ? ' - ' + config.subtitle : ''
 - var tabTitle = is_home() || !pageTitle ? config.title + isSubtitle : pageTitle + ' | ' + config.title
-
-- var pageKeywords
-- if (page.keywords) pageKeywords = Array.isArray(page.keywords) ? (page.keywords).join(',') :  ([]).join(',') || page.keywords
-- else if (page.tags && page.tags.length) pageKeywords = page.tags.data.map(function(tag) {return tag.name;}).join(',')
-- else pageKeywords = Array.isArray(config.keywords) ? (config.keywords).join(','):  ([]).join(',') || config.keywords
 - var pageAuthor = config.email ? config.author + ',' + config.email : config.author
 - var pageCopyright = config.copyright || config.author
 - var themeColorLight = theme.theme_color && theme.theme_color.enable && theme.theme_color.meta_theme_color_light || '#ffffff'
@@ -22,8 +17,6 @@ meta(charset='UTF-8')
 meta(http-equiv="X-UA-Compatible" content="IE=edge")
 meta(name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no")
 title= tabTitle
-if pageKeywords
-  meta(name="keywords" content=pageKeywords)
 meta(name="author" content=pageAuthor)
 meta(name="copyright" content=pageCopyright)
 meta(name ="format-detection" content="telephone=no")