Change name of printer "pausable" -> "not-pausable"

[devtooligan]

Describe the issue:

The results of this printer threw me. It's called "pausable" but it returns all the functions that are not pausable.

Should we have both a "pausable" and "not-pausable"? If not should we update either the logic to reflect the name or else update the arg name?

Code example to reproduce the issue:

https://github.com/crytic/slither/blob/master/slither/printers/summary/when_not_paused.py#L26

class PrinterWhenNotPaused(AbstractPrinter):

    ARGUMENT = "pausable"
    HELP = "Print functions that do not use whenNotPaused"

    WIKI = "https://github.com/trailofbits/slither/wiki/Printer-documentation#when-not-paused"

Version:

0.9.2

Relevant log output:

Constructor and pure/view functions are not displayed

Zero:
+---------------+-------------------+
|      Name     | Use whenNotPaused |
+---------------+-------------------+
| constructor() |                   |
+---------------+-------------------+

One:
+---------------+-------------------+
|      Name     | Use whenNotPaused |
+---------------+-------------------+
| constructor() |                   |
+---------------+-------------------+

Two:
+---------------+-------------------+
|      Name     | Use whenNotPaused |
+---------------+-------------------+
| constructor() |                   |
+---------------+-------------------+

Test:
+----------------+-------------------+
|      Name      | Use whenNotPaused |
+----------------+-------------------+
| constructor()  |                   |
|     test()     |                   |
| test2(uint256) |                   |
| test3(uint256) |                   |
|    test4()     |                   |
+----------------+-------------------+