Fix build script so auto-build of imath uses the new branch name (#1228)

Signed-off-by: Larry Gritz <lg@larrygritz.com>

cmake/OpenEXRSetup.cmake

@@ -251,10 +251,10 @@ option(OPENEXR_FORCE_INTERNAL_IMATH "Force using an internal imath" OFF)
 # Check to see if Imath is installed outside of the current build directory.
 set(IMATH_REPO "https://github.com/AcademySoftwareFoundation/Imath.git" CACHE STRING
     "Repo for auto-build of Imath")
-set(IMATH_TAG "master" CACHE STRING
+set(IMATH_TAG "main" CACHE STRING
   "Tag for auto-build of Imath (branch, tag, or SHA)")
 if(NOT OPENEXR_FORCE_INTERNAL_IMATH)
-  #TODO: ^^ Release should not clone from master, this is a place holder
+  #TODO: ^^ Release should not clone from main, this is a place holder
   set(CMAKE_IGNORE_PATH "${CMAKE_CURRENT_BINARY_DIR}/_deps/imath-src/config;${CMAKE_CURRENT_BINARY_DIR}/_deps/imath-build/config")
   find_package(Imath 3.1)
   set(CMAKE_IGNORE_PATH)