[Docs] Typo fix

[xgupta]

sorry, I don't know the meaning of dwarf. From google search- cause to seem small or insignificant in comparison.

llvm/docs/ProgrammersManual.rst

* a :ref:`bit <ds_bit>` container provides an efficient way to store and
   identifier you want to store.
 
 Once the proper category of container is determined, you can fine tune the
 memory use, constant factors, and cache behaviors of access by intelligently
 picking a member of the category.  Note that constant factors and cache behavior
 can be a big deal.  If you have a vector that usually only contains a few
 elements (but could contain many), for example, it's much better to use
 :ref:`SmallVector <dss_smallvector>` than :ref:`vector <dss_vector>`.  Doing so
-avoids (relatively) expensive malloc/free calls, which dwarf the cost of adding
+avoids (relatively) expensive malloc/free calls, which drop the cost of adding
 the elements to the container.
 
 .. _ds_sequential:
 
 Sequential Containers (std::vector, std::list, etc)
 ---------------------------------------------------
 
 There are a variety of sequential containers available for you, based on your