update DYLD_FALLBACK_LIBRARY_PATH instead of DYLD_LIBRARY_PATH

Per [1]:

       DYLD_LIBRARY_PATH
              This is a colon separated list of directories  that  contain  libraries.  The  dynamic  linker
              searches  these  directories before it searches the default locations for libraries. It allows
              you to test new versions of existing libraries.

              For each library that a program uses, the dynamic linker looks for it  in  each  directory  in
              DYLD_LIBRARY_PATH  in  turn.  If  it still can't find the library, it then searches DYLD_FALL-
              BACK_FRAMEWORK_PATH and DYLD_FALLBACK_LIBRARY_PATH in turn.

              Use the -L option to otool(1).  to discover the frameworks and shared libraries that the  exe-
              cutable is linked against.

       DYLD_FALLBACK_LIBRARY_PATH
              This  is  a  colon  separated  list  of directories that contain libraries.  It is used as the
              default location for libraries not found in their install path.  By  default,  it  is  set  to
              $(HOME)/lib:/usr/local/lib:/lib:/usr/lib.

[1] https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/dyld.1.html