update_engine: fixed warnings from cpplint

Fixed all the cpplint warnings in update engine.

BUG=None
TEST=Unit tests still pass.

Change-Id: I285ae858eec8abe0b26ff203b99a42a200ceb71c
Reviewed-on: https://chromium-review.googlesource.com/204027
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/download_action.h b/download_action.h
index f77f6bc..d2f2004 100644
--- a/download_action.h
+++ b/download_action.h
@@ -83,7 +83,7 @@
 
   // Returns the p2p file id for the file being written or the empty
   // string if we're not writing to a p2p file.
-  std::string p2p_file_id() { return p2p_file_id_; };
+  std::string p2p_file_id() { return p2p_file_id_; }
 
  private:
   // Closes the file descriptor for the p2p file being written and