Added libbz2-dev to Debian based prerequisites

[mttr]

Encountered this when building for the first time today:

note: /usr/bin/ld: cannot find -lbz2
collect2: error: ld returned 1 exit status

error: aborting due to previous error
Could not compile `servo`.

Installing the libbz2-dev packaged fixed it. Added to the list of packages to install on Debian based linuxes in README.md

[hoppipolla-critic-bot]

Critic review: https://critic.hoppipolla.co.uk/r/3222

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[metajack]

Any idea what we have that needs this? Seems very odd.

[mttr]

From what I can tell after grepping my target directory, this seems to be from libfreetype2. A quick search reveals a few references to bzip2 over there.

[jdm]

Yes, @SimonSapin had to get it installed on the build machines after the recent Skia build changes.

[SimonSapin]

Sigh. This is a result of #3980 which did update the README, but then #3991 reverted that change (presumably accidentally).

[SimonSapin]

@mttr, could you also add bzip2 in the corresponding lines for Fedora and Archlinux? See https://github.com/servo/servo/pull/3980/files#diff-1. Thanks!

[Hoverbear]

@SimonSapin Yes it was purely on accident, I didn't check the diff.

[mttr]

@SimonSapin done!

[SimonSapin]

Thanks!

[SimonSapin]

r+

[bors-servo]

saw approval from SimonSapin
at mttr@3b40b51

[bors-servo]

merging mttr/servo/debian_requirements_update = 3b40b51 into auto

[bors-servo]

mttr/servo/debian_requirements_update = 3b40b51 merged ok, testing candidate = df47124

[bors-servo]

all tests pass:
success: http://build.servo.org/builders/linux1/builds/19
success: http://build.servo.org/builders/linux2/builds/19
success: http://build.servo.org/builders/android/builds/86
success: http://build.servo.org/builders/mac1/builds/236
success: http://build.servo.org/builders/mac2/builds/236

[bors-servo]

fast-forwarding master to auto = df47124