text: Title: [Migrated] When no aws_environment_variables are defined in settings, a zappa update will delete any vars defined in the console
  Body: Originally from: https://github.com/Miserlou/Zappa/issues/1010 by [seanpaley](https://github.com/seanpaley)
  
  <!--- Provide a general summary of the issue in the Title above -->
  ## Context
  Title says it - when I have no aws_environment_variables in my zappa_settings.json, any env vars I set manually in the Lambda console disappear on zappa update. If I define one var in the aws_environment_variables dictionary, the vars I manually set persist after an update.
  
  ## Expected Behavior
  Manually defined vars don't get deleted.
  
  ## Actual Behavior
  They get deleted.
  
  ## Possible Fix
  <!--- Not obligatory, but suggest a fix or reason for the bug -->
  
  ## Steps to Reproduce
  <!--- Provide a link to a live example, or an unambiguous set of steps to -->
  <!--- reproduce this bug include code to reproduce, if relevant -->
  
  
  ## Your Environment
  <!--- Include as many relevant details about the environment you experienced the bug in -->
  * Zappa version used: 43.0
  * Operating System and Python version: mac os, python 2.7.13
  * The output of `pip freeze`:
  argcomplete==1.8.2
  base58==0.2.4
  boto3==1.4.4
  botocore==1.5.40
  certifi==2017.4.17
  chardet==3.0.4
  click==6.7
  docutils==0.13.1
  durationpy==0.4
  future==0.16.0
  futures==3.1.1
  hjson==2.0.7
  idna==2.5
  jmespath==0.9.3
  kappa==0.6.0
  lambda-packages==0.16.1
  placebo==0.8.1
  psycopg2==2.7.1
  python-dateutil==2.6.1
  python-slugify==1.2.4
  PyYAML==3.12
  requests==2.18.1
  s3transfer==0.1.10
  six==1.10.0
  toml==0.9.2
  tqdm==4.14.0
  troposphere==1.9.4
  Unidecode==0.4.21
  urllib3==1.21.1
  Werkzeug==0.12
  wsgi-request-logger==0.4.6
  zappa==0.43.0
  
  * Your `zappa_settings.py`: 
  