firefox: Update version from 57.0.2 to 57.0.4

Fixes in 57.0.3 [1]:

> Fix a crash reporting issue that inadvertently sends background tab
> crash reports to Mozilla without user opt-in (bug 1427111)

Fixes in 57.0.4 [2]:

> Security fixes to address the Meltdown and Spectre timing attacks

[1] https://www.mozilla.org/en-US/firefox/57.0.3/releasenotes/
[2] https://www.mozilla.org/en-US/firefox/57.0.4/releasenotes/

firefox.be0

@@ -2,7 +2,7 @@
 
 #export BEE_TMP_TMPDIR=/dev/shm BEE_TMP_BUILDROOT=/dev/shm/bee-root BEE_MAKEFLAGS='-j80'
 
-# BEE_VERSION firefox-57.0.2-1
+# BEE_VERSION firefox-57.0.4-0
 
 SRCURL[0]="https://ftp.mozilla.org/pub/firefox/releases/${PKGVERSION}/source/firefox-${PKGVERSION}.source.tar.xz"