[bug#28560] [PATCH] web: Add try-files for the nginx-service-type.

[Oleg Pykhalov]

Ah, actually I need also to test on real system config before pushed a patch.  
Sorry.

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address@hidden ~/src/guix$ ./pre-inst-env guix system build 
~/dotfiles/guix/system-magnolia.scm 
Backtrace:
In srfi/srfi-1.scm:
   592:29 19 (map1 (#<<service> type: #<service-type mingetty 16f…> …))
   592:29 18 (map1 (#<<service> type: #<service-type mingetty 16f…> …))
   592:29 17 (map1 (#<<service> type: #<service-type console-font…> …))
   592:29 16 (map1 (#<<service> type: #<service-type ntp 1556910>…> …))
   592:29 15 (map1 (#<<service> type: #<service-type dbus 1556a50…> …))
   592:29 14 (map1 (#<<service> type: #<service-type elogind 2d7f…> …))
   592:29 13 (map1 (#<<service> type: #<service-type upower 2d7ff…> …))
   592:29 12 (map1 (#<<service> type: #<service-type avahi 16fe0a…> …))
   592:29 11 (map1 (#<<service> type: #<service-type wpa-supplica…> …))
   592:29 10 (map1 (#<<service> type: #<service-type network-mana…> …))
   592:29  9 (map1 (#<<service> type: #<service-type slim 16fe050…> …))
   592:29  8 (map1 (#<<service> type: #<service-type firewall 2e5…> …))
   592:29  7 (map1 (#<<service> type: #<service-type fcgiwrap 2dd…> …))
   592:17  6 (map1 (#<<service> type: #<service-type nginx 2dd887…> …))
In gnu/services/web.scm:
   317:21  5 (nginx-shepherd-service _)
   308:35  4 (nginx-action . _)
   256:10  3 (default-nginx-config #<package address@hidden gnu/packa…> …)
In srfi/srfi-1.scm:
   592:17  2 (map1 (#<<nginx-server-configuration> http-port: 19418…>))
In gnu/services/web.scm:
    214:9  1 (emit-nginx-server-config _)
In unknown file:
           0 (string-append "      try_files " (("$uri" " ") (# #)) #)

ERROR: In procedure string-append:
ERROR: In procedure string-append: Wrong type (expecting string): (("$uri" " ") 
("@cgit" " "))
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