increment web-server-lib package to version 1.6

This version reflects commits starting with 66b79c8
by Jesse Alama, @mflatt, @Bogdanp, @aymanosman, @samth, and @jeapostrophe:

- Adds many new protections against malicious or misbehaving clients,
  which are controled with a new `safety-limits?` abstraction.

- Adds `response/empty` constructor.

- Fixes bugs with `dispatch/servlet` and HMAC-SHA1 signatures
  for id cookies.

- Allows bytes in addition to strings as arguments to
  `web-server/http/id-cookie` functions for consistency.

web-server-lib/info.rkt

@@ -15,4 +15,4 @@
 
 (define pkg-authors '(jay))
 
-(define version "1.5")
+(define version "1.6")