Not really sure why this is happening.

Build log here:

-----> Node.js app detected
       
-----> Creating runtime environment
       
       NPM_CONFIG_LOGLEVEL=error
       NPM_CONFIG_PRODUCTION=false
       NODE_ENV=production
       NODE_MODULES_CACHE=true
       NODE_VERBOSE=false
       
-----> Installing binaries
       engines.node (package.json):  >=8.9.1
       engines.npm (package.json):   unspecified (use default)
       
       Resolving node version >=8.9.1...
       Downloading and installing node 15.3.0...
       Using default npm version: 7.0.14
       
-----> Installing dependencies
       Installing node modules (package.json)
       npm ERR! code ERESOLVE
       npm ERR! ERESOLVE unable to resolve dependency tree
       npm ERR! 
       npm ERR! While resolving: colyseus-examples@1.0.0
       npm ERR! Found: colyseus@0.14.2
       npm ERR! node_modules/colyseus
       npm ERR!   colyseus@"^0.14.0" from the root project
       npm ERR! 
       npm ERR! Could not resolve dependency:
       npm ERR! peer colyseus@"^0.11.0" from @colyseus/monitor@0.12.2
       npm ERR! node_modules/@colyseus/monitor
       npm ERR!   @colyseus/monitor@"^0.12.1" from the root project
       npm ERR! 
       npm ERR! Fix the upstream dependency conflict, or retry
       npm ERR! this command with --force, or --legacy-peer-deps
       npm ERR! to accept an incorrect (and potentially broken) dependency resolution.
       npm ERR! 
       npm ERR! See /tmp/npmcache.uPmUe/eresolve-report.txt for a full report.
       
       npm ERR! A complete log of this run can be found in:
       npm ERR!     /tmp/npmcache.uPmUe/_logs/2020-11-30T12_49_24_112Z-debug.log
-----> Build failed
       
       We're sorry this build is failing! You can troubleshoot common issues here:
       https://devcenter.heroku.com/articles/troubleshooting-node-deploys
       
       Some possible problems:
       
       - Dangerous semver range (>) in engines.node
         https://devcenter.heroku.com/articles/nodejs-support#specifying-a-node-js-version
       
       Love,
       Heroku
       
 !     Push rejected, failed to compile Node.js app.
 !     Push failed