Do not display a warning when the .env file does not exist

[sgerbino]

Resolves #153.

Brief description

Removes the warning when the .env does not exist.

Checklist

• I have built this pull request locally
• I have ran the unit tests locally
• I have manually tested this pull request
• I have reviewed my pull request
• I have added any relevant tests

Demonstration

❯ ./koinos-cli/build/koinoscli
Connected to endpoint https://api.koinos.io/

Token 'koin' at address 15DJN4a8SgrbGhhGksSBASiSYjGnMU8dGL registered

Token 'vhp' at address 1AdzuXSpC6K9qtXdCBgD5NUpDNwHjMgrc9 registered

Contract 'pob' at address 159myq5YUhhoVWu3wsHKHiJYKPKGUrGiyv registered

Contract 'name_service' at address 19WxDJ9Kcvx4VqQFkpwVmwVEy1hMuwXtQE registered

Koinos CLI v1.0.0
Type "list" for a list of commands, "help <command>" for help on a specific command.
🔐 > exit