Add bc dependency

Screenfetch doesn't work properly unless we install our version of bc.

If readline is installed from Chromebrew the stock version of bc starts
throwing errors related to libreadline.

packages/screenfetch.rb

@@ -3,23 +3,17 @@ require 'package'
 class Screenfetch < Package
   description 'Fetches system/theme information in terminal for Linux desktop screenshots.'
   homepage 'https://github.com/KittyKatt/screenFetch'
-  version '3.8.0'
+  version '3.8.0-1'
   source_url 'https://github.com/KittyKatt/screenFetch/archive/v3.8.0.tar.gz'
   source_sha256 '248283ee3c24b0dbffb79ed685bdd518554073090c1c167d07ad2a729db26633'
 
   binary_url ({
-    aarch64: 'https://dl.bintray.com/chromebrew/chromebrew/screenfetch-3.8.0-chromeos-armv7l.tar.xz',
-     armv7l: 'https://dl.bintray.com/chromebrew/chromebrew/screenfetch-3.8.0-chromeos-armv7l.tar.xz',
-       i686: 'https://dl.bintray.com/chromebrew/chromebrew/screenfetch-3.8.0-chromeos-i686.tar.xz',
-     x86_64: 'https://dl.bintray.com/chromebrew/chromebrew/screenfetch-3.8.0-chromeos-x86_64.tar.xz',
   })
   binary_sha256 ({
-    aarch64: 'd728b9a8b6b3ef433587826f243c372a7589b84df0adcb4280199d7f771ee6ab',
-     armv7l: 'd728b9a8b6b3ef433587826f243c372a7589b84df0adcb4280199d7f771ee6ab',
-       i686: 'c8e6b6aadbe2d56b87c9866b437d8e794815c7331cd8d692573712d07d41d95d',
-     x86_64: '0c90ff765e88b492e37bb101d5ee95443586c3a2555ccccb5bf5bd0f8da892d2',
   })
 
+  depends_on 'bc'
+
   def self.build
   end