check sharp module already loaded

[dkrnl]

Hi!
More readable error if sharp already loaded in peer deps.

e.g.:

test.js

const favicons = require('favicons'); 
const sharp = require('sharp');

output:

node ./test.js

Something went wrong installing the "sharp" module

The specified procedure could not be found.
\\?\/home/sharp-something-wrong/node_modules/sharp/build/Release/sharp-win32-x64.node

Possible solutions:
- Install with the --verbose flag and look for errors: "npm install --ignore-scripts=false --verbose sharp"
- Install for the current runtime: "npm install --platform=win32 --arch=x64 sharp"
- Consult the installation documentation: https://sharp.pixelplumbing.com/install
- Module already loaded in: /home/sharp-something-wrong/node_modules/favicons/node_modules/sharp/build/Release/sharp.node

npm ls sharp

+-- favicons-webpack-plugin@5.0.2
| `-- favicons@6.2.2
|   `-- sharp@0.28.3
`-- sharp@0.29.1

[lovell]

Hi, thank you for this PR, it will definitely make a useful addition to the help.

Please can you make this Windows only, and perhaps modify the solution message to read something like "Ensure version aligns with".

[dkrnl]

Ok. fixed.

[coveralls]

Coverage remained the same at 100.0% when pulling 2ea9a3e on dkrnl:master into f37ca82 on lovell:master.

[lovell]

Thank you!