Fix #61 Error: Cannot find module 'rollup/bin/rollup'

[andrericardo]

Based on bin path in https://github.com/chartjs/Chart.js/blob/master/gulpfile.js

Thanks for contributing.

• Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1

Description

Changed the path of rollup

PS: I've only just noticed that this is also failing master in Travis after the version bump commit
https://travis-ci.org/chartjs/chartjs-chart-financial/builds/591814183#L498

Testing

Sorry I don't know yet how to test a gulp file method properly, here is a screenshot of the build working.

The error

gulp build

[00:45:51] Using gulpfile ~/VirtualBox/Win10/chartjs-chart-financial/gulpfile.js
[00:45:51] Starting 'build'...
[00:45:51] Starting 'rollupTask'...
[00:45:51] 'rollupTask' errored after 4.01 ms
[00:45:51] Error: Cannot find module 'rollup/bin/rollup'
at Function.Module._resolveFilename (internal/modules/cjs/loader.js:613:15)
at Function.resolve (internal/modules/cjs/helpers.js:28:19)
at run (/Users/andre/VirtualBox/Win10/chartjs-chart-financial/gulpfile.js:42:21)
at rollupTask (/Users/andre/VirtualBox/Win10/chartjs-chart-financial/gulpfile.js:51:3)
at bound (domain.js:400:14)
at runBound (domain.js:413:12)
at asyncRunner (/Users/andre/VirtualBox/Win10/chartjs-chart-financial/node_modules/async-done/index.js:55:18)
at processTicksAndRejections (internal/process/next_tick.js:74:9)
[00:45:51] 'build' errored after 10 ms