remove link in blog post 'pruning' (fix jekyll error)
the 'author' field in !989 (merged) contains a link in markdown, which is not accepted by jekyll (in that header). Fixes the error Error: could not read file /var/www/getmonero.org/core/_posts/2019-02-01-pruning.md: (<unknown>): did not find expected key while parsing a block mapping at line 2 column 1