update_engine: fixed remaining linter and some spelling errors

Fixed remaining errors from cpplint as well as some spelling errors
mostly in comments.

BUG=None
TEST=FEATURES=test emerge-link update_engine

Change-Id: I484988ab846ac5a3c68c016ddccfb247f225ec27
Reviewed-on: https://chromium-review.googlesource.com/208897
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/update_manager/generic_variables.h b/update_manager/generic_variables.h
index 9d00b7e..ad9f0c1 100644
--- a/update_manager/generic_variables.h
+++ b/update_manager/generic_variables.h
@@ -153,7 +153,7 @@
 // SetValue and UnsetValue to modify the current value of the variable and
 // notify the registered observers whenever the value changed.
 //
-// The type T needs to be copy-constructable, default-constructable and have an
+// The type T needs to be copy-constructible, default-constructible and have an
 // operator== (to determine if the value changed), which makes this class
 // suitable for basic types.
 template<typename T>