chore: update Doxyfile (#162)

efficively -> effectively

Authors:
  - Ikko Eltociear Ashimine (https://github.com/eltociear)

Approvers:
  - Corey J. Nolet (https://github.com/cjnolet)

URL: rapidsai/cuvs#162

cpp/doxygen/Doxyfile

@@ -454,7 +454,7 @@ LOOKUP_CACHE_SIZE      = 0
 # than 0 to get more control over the balance between CPU load and processing
 # speed. At this moment only the input processing can be done using multiple
 # threads. Since this is still an experimental feature the default is set to 1,
-# which efficively disables parallel processing. Please report any issues you
+# which effectively disables parallel processing. Please report any issues you
 # encounter. Generating dot graphs in parallel is controlled by the
 # DOT_NUM_THREADS setting.
 # Minimum value: 0, maximum value: 32, default value: 1.