Update OpenSfM, bump version

SuperBuild/cmake/External-OpenSfM.cmake

@@ -19,7 +19,7 @@ ExternalProject_Add(${_proj_name}
   #--Download step--------------
   DOWNLOAD_DIR      ${SB_DOWNLOAD_DIR}
   GIT_REPOSITORY    https://github.com/OpenDroneMap/OpenSfM/
-  GIT_TAG           283
+  GIT_TAG           284
   #--Update/Patch step----------
   UPDATE_COMMAND    git submodule update --init --recursive
   #--Configure step-------------

VERSION

@@ -1 +1 @@
-2.8.3
+2.8.4