share: remove site baseurl

`{{.Permalink}}` has the base URL in the permalink already. I just
removed the `{{.Site.BaseURL}}`, but
`{{.Site.BaseURL}}{{.RelPermalink}}` could work too.

layouts/partials/share.html

@@ -1,4 +1,4 @@
-<a class="twitter" href="https://twitter.com/intent/tweet?text={{ .Site.BaseURL }}{{ .Permalink }} - {{ .Title }} {{ with .Site.Params.twitter }}by @{{ . }}{{ end }}"><span class="icon-twitter"> {{ with .Site.Params.tweet }}{{ . }}{{ else }}Tweet{{ end }}</span></a>
+<a class="twitter" href="https://twitter.com/intent/tweet?text={{ .Permalink }} - {{ .Title }} {{ with .Site.Params.twitter }}by @{{ . }}{{ end }}"><span class="icon-twitter"> {{ with .Site.Params.tweet }}{{ . }}{{ else }}Tweet{{ end }}</span></a>
 
 <a class="facebook" href="#" onclick="
     window.open(
@@ -6,4 +6,4 @@
       'facebook-share-dialog',
       'width=626,height=436');
     return false;"><span class="icon-facebook-rect"> {{ with .Site.Params.share }}{{ . }}{{ else }}Share{{ end }}</span>
-</a>
+</a>