nghttp2: bump to 1.38.0

nghttp2: bump to 1.38.0

4a9d2005 Update manual pages
acf6a922 Bump up version number to 1.38.0, LT revision to 31:3:17
4ff45821 Update AUTHORS
42dce01e Merge branch 'nghttpx-fix-backend-selection-on-retry'
a35059e3 nghttpx: Fix bug that altered authority and path affect backend selection
5a30fafd Merge branch 'nghttpx-fix-chunked-request-stall'
dce91ad3 Merge branch 'nghttpx-dont-log-authorization'
2cff8b43 nghttpx: Fix bug that chunked request stalls
be96654d nghttpx: Don't log authorization request header field value with -LINFO
ce962c3f Merge branch 'update-http-parser'
f931504e Update http-parser to v2.9.1
d978f351 Fix bug that on_header callback is still called after stream is closed
ec519f22 Merge pull request #1270 from baitisj/master
e8b213e3 Bump up version number to 1.38.0-DEV

Signed-off-by: Hans Dedecker <dedeckeh@gmail.com>