does not link on ubuntu 14.04, fix provided

Hi,

unfortunately static linking gives problems on Ubuntu 14.04 so I modified the Makefile to build a dynamic binary on linux.

Here is my relevant commit:
https://github.com/jazzkutya/morse/commit/c434945b6eb5564fffe89241912131f8e6dc6b5d
I hope you find it useful.

Best,
hg2eck
