Update dependencies cli-helpers, prompt-toolkit, and sqlparse.

mssql-cli depends on old version of cli-helpers, prompt-toolkit, and sqlparse, which are incompatible with the newer versions that are required by pgcli 3.0.0. Is it possible to update these libraries?

```
ERROR: pgcli 3.0.0 has requirement cli-helpers[styles]>=1.2.0, but you'll have cli-helpers 0.2.3 which is incompatible.
ERROR: pgcli 3.0.0 has requirement prompt-toolkit<4.0.0,>=3.0.0, but you'll have prompt-toolkit 2.0.10 which is incompatible.
ERROR: pgcli 3.0.0 has requirement sqlparse<0.4,>=0.3.0, but you'll have sqlparse 0.2.4 which is incompatible.
```

**Full output**
```
> pip install mssql-cli
Defaulting to user installation because normal site-packages is not writeable
Requirement already satisfied: mssql-cli in ./.local/lib/python3.8/site-packages (1.0.0)
Requirement already satisfied: humanize>=0.5.1 in ./.local/lib/python3.8/site-packages (from mssql-cli) (2.4.0)
Requirement already satisfied: configobj>=5.0.6 in ./.local/lib/python3.8/site-packages (from mssql-cli) (5.0.6)
Collecting cli-helpers<1.0.0,>=0.2.3
Using cached cli_helpers-0.2.3-py2.py3-none-any.whl (26 kB)
Requirement already satisfied: enum34>=1.1.6 in ./.local/lib/python3.8/site-packages (from mssql-cli) (1.1.10)
Requirement already satisfied: future>=0.16.0 in /usr/lib/python3/dist-packages (from mssql-cli) (0.18.2)
Requirement already satisfied: wheel>=0.29.0 in /usr/lib/python3/dist-packages (from mssql-cli) (0.34.2)
Requirement already satisfied: applicationinsights>=0.11.1 in ./.local/lib/python3.8/site-packages (from mssql-cli) (0.11.9)
Collecting prompt-toolkit<2.1.0,>=2.0.0
Using cached prompt_toolkit-2.0.10-py3-none-any.whl (340 kB)
Requirement already satisfied: Pygments>=2.0 in ./.local/lib/python3.8/site-packages (from mssql-cli) (2.6.1)
Collecting sqlparse<0.3.0,>=0.2.2
Using cached sqlparse-0.2.4-py2.py3-none-any.whl (38 kB)
Requirement already satisfied: click<7.1,>=4.1 in ./.local/lib/python3.8/site-packages (from mssql-cli) (7.0)
Requirement already satisfied: argparse>=1.2.1 in ./.local/lib/python3.8/site-packages (from mssql-cli) (1.4.0)
Requirement already satisfied: six in ./.local/lib/python3.8/site-packages (from configobj>=5.0.6->mssql-cli) (1.15.0)
Requirement already satisfied: backports.csv>=1.0.0 in ./.local/lib/python3.8/site-packages (from cli-helpers<1.0.0,>=0.2.3->mssql-cli) (1.0.7)
Requirement already satisfied: terminaltables>=3.0.0 in ./.local/lib/python3.8/site-packages (from cli-helpers<1.0.0,>=0.2.3->mssql-cli) (3.1.0)
Requirement already satisfied: wcwidth in ./.local/lib/python3.8/site-packages (from prompt-toolkit<2.1.0,>=2.0.0->mssql-cli) (0.2.4)
ERROR: pgcli 3.0.0 has requirement cli-helpers[styles]>=1.2.0, but you'll have cli-helpers 0.2.3 which is incompatible.
ERROR: pgcli 3.0.0 has requirement prompt-toolkit<4.0.0,>=3.0.0, but you'll have prompt-toolkit 2.0.10 which is incompatible.
ERROR: pgcli 3.0.0 has requirement sqlparse<0.4,>=0.3.0, but you'll have sqlparse 0.2.4 which is incompatible.
Installing collected packages: cli-helpers, prompt-toolkit, sqlparse
Attempting uninstall: cli-helpers
Found existing installation: cli-helpers 2.0.1
Uninstalling cli-helpers-2.0.1:
Successfully uninstalled cli-helpers-2.0.1
Attempting uninstall: prompt-toolkit
Found existing installation: prompt-toolkit 3.0.5
Uninstalling prompt-toolkit-3.0.5:
Successfully uninstalled prompt-toolkit-3.0.5
Attempting uninstall: sqlparse
Found existing installation: sqlparse 0.3.1
Uninstalling sqlparse-0.3.1:
Successfully uninstalled sqlparse-0.3.1
Successfully installed cli-helpers-0.2.3 prompt-toolkit-2.0.10 sqlparse-0.2.4
```
**Environment**
```
> python -V
Python 3.8.2
> which python
/usr/bin/python
> pip -V
pip 20.1.1 from /home/jumpnett/.local/lib/python3.8/site-packages/pip (python 3.8)
> which pip
/usr/local/bin/pip
```

Start by locating mssql-cli's dependency declarations for cli-helpers, prompt-toolkit, and sqlparse. Check the package constraints against the versions required by pgcli 3.0.0, then run the project's installation or CLI tests. Done means installation no longer downgrades these libraries into incompatible versions and the client still works.

Written by the indexing model from the issue text.