Config.observe is deprecated.

[rochacbruno]

Config::observe no longer takes a callNow option. Use ::onDidChange instead.
Note that ::onDidChange passes its callback different arguments.
See https://atom.io/docs/api/latest/Config

Config.observe (/usr/share/atom/resources/app.asar/src/config.js:126:16)
Object.activate (/home/rochacbruno/.atom/packages/flake8/lib/flake8.coffee:118:16)
Package.activateNow (/usr/share/atom/resources/app.asar/src/package.js:238:19)
<unknown> (/usr/share/atom/resources/app.asar/src/package.js:219:30)
Package.measure (/usr/share/atom/resources/app.asar/src/package.js:163:15)
Package.activate (/usr/share/atom/resources/app.asar/src/package.js:211:14)