Fix NekPy install path
Fixes NekPy install paths; lack of INSTALL command meant libraries were linked against the build location vs. their install location, so would break when using nekpy-install-user or nekpy-install-system.
Fixes NekPy install paths; lack of INSTALL command meant libraries were linked against the build location vs. their install location, so would break when using nekpy-install-user or nekpy-install-system.