worker: Redirect stderr of split command to stdout

Usually RSpec prints errors to stderr, so we have to grab it too in
order to display a helpful error message in case this command fails.

Ideally we'd do this with popen3, but this is good enough for now,
considering #6.

lib/rspecq/worker.rb

@@ -163,13 +163,10 @@ def reset_rspec_state!
     # Their errors will be reported in the normal flow, when they're picked up
     # as jobs by a worker.
     def files_to_example_ids(files)
-      # TODO: do this programatically
-      cmd = "DISABLE_SPRING=1 bundle exec rspec --dry-run --format json #{files.join(' ')}"
+      cmd = "DISABLE_SPRING=1 bundle exec rspec --dry-run --format json #{files.join(' ')} 2>&1"
       out = `#{cmd}`
 
       if !$?.success?
-        puts out
-        puts $?.inspect
         rspec_output = begin
           JSON.parse(out)
         rescue JSON::ParserError
@@ -184,7 +181,6 @@ def files_to_example_ids(files)
         )
 
         pp rspec_output
-        puts
 
         return files
       end
@@ -201,6 +197,8 @@ def elapsed(since)
       Process.clock_gettime(Process::CLOCK_MONOTONIC) - since
     end
 
+    # Prints msg to standard output and emits an event to Sentry, if the
+    # SENTRY_DSN environment variable is set.
     def log_event(msg, level, additional={})
       puts msg