build(deps): bump github.com/itzg/go-flagsfiller from 1.4.2 to 1.8.0

Bumps [github.com/itzg/go-flagsfiller](https://github.com/itzg/go-flagsfiller) from 1.4.2 to 1.8.0.
- [Release notes](https://github.com/itzg/go-flagsfiller/releases)
- [Commits](itzg/go-flagsfiller@v1.4.2...v1.8.0)

---
updated-dependencies:
- dependency-name: github.com/itzg/go-flagsfiller
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

go.mod

@@ -3,7 +3,7 @@ module github.com/itzg/saml-auth-proxy
 require (
 	github.com/crewjam/saml v0.4.6
 	github.com/iancoleman/strcase v0.2.0 // indirect
-	github.com/itzg/go-flagsfiller v1.4.2
+	github.com/itzg/go-flagsfiller v1.8.0
 	github.com/patrickmn/go-cache v2.1.0+incompatible
 	golang.org/x/crypto v0.0.0-20210711020723-a769d52b0f97 // indirect
 )

go.sum

@@ -16,8 +16,8 @@ github.com/google/go-cmp v0.5.6/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/
 github.com/iancoleman/strcase v0.0.0-20191112232945-16388991a334/go.mod h1:SK73tn/9oHe+/Y0h39VT4UCxmurVJkR5NA7kMEAOgSE=
 github.com/iancoleman/strcase v0.2.0 h1:05I4QRnGpI0m37iZQRuskXh+w77mr6Z41lwQzuHLwW0=
 github.com/iancoleman/strcase v0.2.0/go.mod h1:iwCmte+B7n89clKwxIoIXy/HfoL7AsD47ZCWhYzw7ho=
-github.com/itzg/go-flagsfiller v1.4.2 h1:aQRyQ9/ps111FZYGhzxgKYiOewE7zbAks7rxF49Qlm8=
-github.com/itzg/go-flagsfiller v1.4.2/go.mod h1:mfQgTahSs4OHn8PYev2Wwi1LJXUiYiGuZVCpBLxzbYs=
+github.com/itzg/go-flagsfiller v1.8.0 h1:e6K0N4lzYQc6y9QoCMzVwpg+YHKrMVW3mqiE9bwkQ9U=
+github.com/itzg/go-flagsfiller v1.8.0/go.mod h1:mfQgTahSs4OHn8PYev2Wwi1LJXUiYiGuZVCpBLxzbYs=
 github.com/jonboulle/clockwork v0.2.2 h1:UOGuzwb1PwsrDAObMuhUnj0p5ULPj8V/xJ7Kx9qUBdQ=
 github.com/jonboulle/clockwork v0.2.2/go.mod h1:Pkfl5aHPm1nk2H9h0bjmnJD/BcgbGXUBGnn1kMkgxc8=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=