issue when no API_VERSION is given

[Cyril Diagne]

Steps:

• Run kuda generate
• The generated skaffold file makes use of an undefined API_VERSION environment variable
• Call skaffold dev fails with this error:

 failed: generating tag for <redacted>: executing template: temp
late: envTemplate:1:18: executing "envTemplate" at <.API_VERSION>: map has no entry for key "API_VERSION" 

Workaround:

• Manually export an API_VERSION before running skaffold dev: API_VERSION=0.1.0 && skaffold dev