Fetcher: switch us back to the wget fetcher
Fetcher: switch us back to the wget fetcher

Commit b1eb547275, which added the serf fetcher, broke fetching.  For now,
switch back to the wget fetcher.

digideskio/ngx_pagespeed,digideskio/ngx_pagespeed,pagespeed/ngx_pagespeed,wanrui/ngx_pagespeed,0x0mar/ngx_pagespeed,0x0mar/ngx_pagespeed,pagespeed/ngx_pagespeed,wanrui/ngx_pagespeed