Please update dependency upperbounds

[ezzieyguywuf]

In order to maintain the gentoo package of idris, we have had to manually bump the versions of the following packages:

• aeson to aeson-1.5
• 'optparse-applicativetooptparse-applicative-0.16.1.0`

We have succesfully compiled and run the test-suite using these versions and ghc-8.10.3.

Can you bump these versions in the cabal file and release a new version? This will allow us to better support the gentoo package of this project.

[ezzieyguywuf]

Also add megaparsec to this list.

[Jake-Gillberg]

looks like the plan is to stick to megaparsec < 9: https://github.com/idris-lang/Idris-dev/issues/4826