Fix DEV always being false in webpack

[marvinhagemeister]

Found this while debugging why prop-types didn't work in preact-cli (see: preactjs/preact-cli#627).

Turns out the reason is that our global DEV variable was always set to false when preact-compat was bundled. The reason being that we checked if process is available:

const DEV = typeof process !== 'undefined' && process.env && process.env.NODE_ENV!=='production';

But bundlers typically don't shim the process object and instead replace all string occurrences of process.env.NODE_ENV with development for example. After the bundler has done its magic the code would now look like this:

const DEV = typeof process !== 'undefined' && process.env && 'development'!=='production';

Note that process is still undefined which is why DEV will always be false.

[developit]

released in 3.18.4!