Revert "Revert "Try a longer timeout""

This reverts commit 792d377.

Actually, I've seen some of these timeouts since I reverted it, so maybe
the longer timeout was useful. Let's see.

Author: jonleighton

lib/spring/client/run.rb

@@ -7,7 +7,7 @@ module Client
     class Run < Command
       FORWARDED_SIGNALS = %w(INT QUIT USR1 USR2 INFO WINCH) & Signal.list.keys
       CONNECT_TIMEOUT   = 1
-      BOOT_TIMEOUT      = 10
+      BOOT_TIMEOUT      = 20
 
       attr_reader :server