Ran into same issue with Yaws 1.96 and Erlang R16B01 
in Linux x86_64...

compile: warnings being treated as errors
yaws_websockets.erl:1250: crypto:sha/1 is deprecated and will be removed in in a future release; use crypto:hash/2
make[1]: *** [../ebin/yaws_websockets.beam] Error 1
make[1]: Leaving directory `/home/ajam/Downloads/yaws-1.96/src'
make: *** [all] Error 1

As the error states, the only issue is with
line 1250 in src/yaws_websockets.erl.

Changed "HashBin = crypto:sha(Salted),"

...for...

"HashBin = crypto:hash(sha, Salted),"

...and completed the compile and install without
any issues. Seems to be running fine. Nevertheless,
glad to know "this is already fixed on github master." Thanks!