Syntax Error when running any command

**1. Please specify the following:**
- OS: OSX ___
- Shell: zsh ____

**2. Description**
After installing the CLI, as described in the docs I get the following error when I run "any" eb command:

```
Traceback (most recent call last):
File "/Users/####/.ebcli-virtual-env/executables/eb", line 41, in
execfile(activate_this, dict(__file__=activate_this))
File "/Users/####/.ebcli-virtual-env/bin/activate_this.py", line 18
raise AssertionError(msg) from exc
^
SyntaxError: invalid syntax
```

Reproduce the installation on OSX with zsh, then inspect the generated .ebcli-virtual-env/bin/activate_this.py and the executables/eb traceback shown in the report. Confirm the Python compatibility involved and verify that running an eb command after installation no longer raises the SyntaxError.

Written by the indexing model from the issue text.