Upgrade gomod libraries to address security vulnerabilities

[mindaugasrukas]

Address #186

go get -u golang.org/x/net
go get -u github.com/Masterminds/sprig

After upgrade:

 % trivy filesystem .
2023-05-26T11:22:33.734-0700	INFO	Vulnerability scanning is enabled
2023-05-26T11:22:33.734-0700	INFO	Secret scanning is enabled
2023-05-26T11:22:33.734-0700	INFO	If your scanning is slow, please try '--scanners vuln' to disable secret scanning
2023-05-26T11:22:33.734-0700	INFO	Please see also https://aquasecurity.github.io/trivy/v0.41/docs/secret/scanning/#recommendation for faster secret detection
2023-05-26T11:22:34.147-0700	INFO	Number of language-specific files: 1
2023-05-26T11:22:34.147-0700	INFO	Detecting gomod vulnerabilities...