Update swagger definition for envVars
Update swagger definition for envVars

EnvVars are incorrectly marked as arrays and this is causing some
confusion. Made a fix with Ivana reviewing and tested in Swagger
UI. https://github.com/openfaas/faas-netes/issues/204

Signed-off-by: Alex Ellis (VMware) <5f7133baa0f5c7ca63ff11e11f2e2b0d2cf077c8@gmail.com>

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