Fix long time bug in shell commands

Running a Shell command with the built in shell utility only returns
a single line of the result on either STDOUT or STDERR. This commit
fixes this to return all output from the running of a command or
commands.

lib/java_buildpack/util/shell.rb

@@ -31,8 +31,8 @@ def shell(*args)
         Open3.popen3(*args) do |_stdin, stdout, stderr, wait_thr|
           if wait_thr.value != 0
             puts "\nCommand '#{args.join ' '}' has failed"
-            puts "STDOUT: #{stdout.gets}"
-            puts "STDERR: #{stderr.gets}"
+            puts "STDOUT: #{stdout.gets nil}"
+            puts "STDERR: #{stderr.gets nil}"
 
             fail
           end