vibed/web-server.md code example build error.

[VGeo]

The WEB Server example building fails with

source/app.d(51,9): Error: invalid `foreach` aggregate `req.headers`, define `opApply()`, range primitives, or use `.tupleof`

DMD64 D Compiler v2.097.2, vibe.d 0.9.3

Could be fixed with byKeyValue() method:

foreach(key, value; req.headers.byKeyValue()) {

[Hume2]

It happens with DMD 2.100.0 also. Additionally, it requires to cast the variable username_ to string using cast(string)username_.