Removed the prepended number from remote_version and checksum

nvm_remote_version returns __5:v0.10.2__. When that is substituted to form the node filename __node-5:v0.10.2-darwin-x86_64.tar.gz__. I used pattern substitution to remove the prepended number and colon.

The same problem appears for comparing checksums. The first checksum argument would return __foo__ while the second argument returns __1:foo__. I used the same technique to remove the prepended number and colon.

Please feel free to improve the shell code.