SyntaxError: future feature annotations is not defined

**1. Please specify the following:**
- OS: Ubuntu 20.04
- Shell: Bash

**2. Description**
After successfully installing `eb` and running `eb` in bash it returns:
```bash
root@me:~# eb
Traceback (most recent call last):
File "/root/.ebcli-virtual-env/executables/eb", line 41, in
execfile(activate_this, dict(__file__=activate_this))
File "/root/.ebcli-virtual-env/bin/activate_this.py", line 7
from __future__ import annotations
SyntaxError: future feature annotations is not defined
```

Reproduce the installation on Ubuntu 20.04 with Bash, then inspect the generated /root/.ebcli-virtual-env/bin/activate_this.py and /root/.ebcli-virtual-env/executables/eb paths shown in the traceback. Done means invoking eb starts successfully without the Python SyntaxError.

Written by the indexing model from the issue text.