Injecting configuration and compiling...
[1G [1G-----> Node.js app detected
[1G
[1G-----> Creating runtime environment
[1G
[1G NPM_CONFIG_LOGLEVEL=error
[1G NPM_CONFIG_PRODUCTION=true
[1G NPM_CONFIG_CAFILE=/etc/ssl/certs/ca-certificates.crt
[1G NODE_VERBOSE=false
[1G NODE_ENV=production
[1G NODE_TLS_REJECT_UNAUTHORIZED=0
[1G NODE_MODULES_CACHE=true
[1G
[1G-----> Installing binaries
[1G engines.node (package.json): unspecified
[1G engines.npm (package.json): unspecified (use default)
[1G
[1G Resolving node version 6.x...
[1G Error: Invalid semantic version "6.x"
[1G
[1G-----> Build failed
[1G
[1G ! Invalid semver requirement
[1G
[1G Node, Yarn, and npm adhere to semver, the semantic versioning convention
[1G popularized by GitHub.
[1G
[1G http://semver.org/
[1G
[1G However you have specified a version requirement that is not a valid
[1G semantic version.
[1G
[1G https://kb.heroku.com/why-is-my-node-js-build-failing-because-of-an-invalid-semver-requirement
[1G