support go 1.18

[ks6088ts]

What this PR does / why we need it:

Before anything else, thank you for creating the tool, which helps my daily tasks a lot. :)
When I switched to go 1.18. I failed to install sesstok on darwin/arm64 as follows.

❯ go version
go version go1.18 darwin/arm64

❯ go install github.com/moznion/sesstok/cmd/sesstok@latest
# golang.org/x/sys/unix
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:28:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:43:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:59:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:75:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:90:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:105:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:121:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:136:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:151:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:166:3: //go:linkname must refer to declared function or variable
../../../../1.18.0/pkg/mod/golang.org/x/[email protected]/unix/zsyscall_darwin_arm64.go:166:3: too many errors

To fix the above issue, I just bumped golang.org/x/sys and added some minor fixes.

Additional documentation

I found similar issue here.

[ks6088ts]

I confirmed a binary built on go 1.18 works fine by the following procedures. But I'm not sure whether I should update release.yml to 1.18.

❯ make build VERSION=tmp
❯ ./bin/sesstok_darwin_arm64_tmp
rc file path: /Users/shinji/.sesstok.rc
rc file doesn't exist
would you like initialize? [N/y] y
would you like to set a master password? [N/y] y
master password:
master password (confirm):
access key ID for assume role: hoge
secret access key for assume role: hoge
MFA serial (ARN): hoge
profile name for assume role: hoge
initialized (created rc file: /Users/shinji/.sesstok.rc)
OK, please retry this command with token code :)

[moznion]

Thanks for doing this.