message: [Doc] Bump Doxyfile to pre-2.2
  Now that 2.1.7 has been branched off, master is 2.1.99 (pre-2.2).
diff: @@ -34,7 +34,7 @@ PROJECT_NAME = PIVX
  # This could be handy for archiving the generated documentation or
  # if some version control system is used.
  -PROJECT_NUMBER = 2.1.7
  +PROJECT_NUMBER = 2.1.99
  # Using the PROJECT_BRIEF tag one can provide an optional one line description
  # for a project that appears at the top of each page and should give viewer
  