`make install` does not work on mac

[j-krose]

When running make install on MacOS I was get the following output:

% make install
which ronn && make update_docs || true
install -D build/focus-stack "/usr/local/bin/focus-stack"
usage: install [-bCcpSsUv] [-f flags] [-g group] [-m mode] [-o owner]
               [-M log] [-D dest] [-h hash] [-T tags]
               [-B suffix] [-l linkflags] [-N dbdir]
               file1 file2
       install [-bCcpSsUv] [-f flags] [-g group] [-m mode] [-o owner]
               [-M log] [-D dest] [-h hash] [-T tags]
               [-B suffix] [-l linkflags] [-N dbdir]
               file1 ... fileN directory
       install -dU [-vU] [-g group] [-m mode] [-N dbdir] [-o owner]
               [-M log] [-D dest] [-h hash] [-T tags]
               directory ...
make: *** [install] Error 64

[j-krose]

Made change #62 to fix this