Update curl-sys dependency requirement
          #7464
        
          
      
                
     Merged
            
            
          
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Pulls in alexcrichton/curl-rust#304 which fixes a bug from the last curl
update in #7308. This bug was not introduced by the Cargo PR itself but
rather by updating the
curlsubmodule in thecurl-syscrate. Withoutthis bugfix all downloads of a crate will make a new connection to
crates.io, which drastically increases download time since setting up a
connection takes so long.