Recreate mod files to reduce indirect dependencies

[bbrks]

Fixes #1

Recreated mod files to remove the unused/indirect dependencies, and bumped versions:

• Removed all dependencies not required for building the project
• Bumped github.com/prometheus/client_golang from v1.0.0 to v1.2.1

Steps ran to get to this point:

$ rm go.mod
$ rm go.sum
$ go mod init
$ go mod tidy

Allows project to be buildable out of the box:

$ git clone --branch bump_deps git@github.com:bbrks/fping-exporter.git bbrks-fping-exporter
Cloning into 'bbrks-fping-exporter'...
remote: Enumerating objects: 44, done.
remote: Counting objects: 100% (44/44), done.
remote: Compressing objects: 100% (32/32), done.
remote: Total 44 (delta 16), reused 36 (delta 11), pack-reused 0
Receiving objects: 100% (44/44), 280.09 KiB | 647.00 KiB/s, done.
Resolving deltas: 100% (16/16), done.
$ cd bbrks-fping-exporter/
$ go build
$ ls -l fping-exporter
.rwxr-xr-x 11M bbrks  6 Nov 13:06 fping-exporter*

[schweikert]

Thanks!