Bump github.com/spf13/afero from 1.5.1 to 1.6.0 (#33)

Bumps [github.com/spf13/afero](https://github.com/spf13/afero) from 1.5.1 to 1.6.0.
- [Release notes](https://github.com/spf13/afero/releases)
- [Commits](https://github.com/spf13/afero/compare/v1.5.1...v1.6.0)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

go.mod

@@ -12,7 +12,7 @@ require (
 	github.com/mmcdole/gofeed v1.1.0
 	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
 	github.com/nsf/termbox-go v0.0.0-20200204031403-4d2b513ad8be // indirect
-	github.com/spf13/afero v1.5.1
+	github.com/spf13/afero v1.6.0
 	github.com/stretchr/testify v1.7.0
 	golang.org/x/net v0.0.0-20200324143707-d3edc9973b7e // indirect
 	gopkg.in/check.v1 v1.0.0-20200227125254-8fa46927fb4f // indirect