nave install/use version - Fails to install node if user has a shell alias or function called `shasum`

[DavidPesticcio]

Suggest using absolute path for shasum in nave.sh at line 226

Adding absolute path for shasum resolves this issue.

FYI: The command not found error below is from my shell function not nave.sh 😉

$ nave install 21.0.0
############################################################################################################################################################################################################ 100.0%
dirname: invalid option -- 'a'
Try 'dirname --help' for more information.
environment: line 13: -asum: command not found
shasum mismatch, expect 013f370f1772197cb4e22f22f2185ee26d2e5f3acdb2f252d11cd214e9a8cdb9, got Checking:
Binary install failed, trying source.
############################################################################################################################################################################################################ 100.0%
dirname: invalid option -- 'a'
Try 'dirname --help' for more information.
environment: line 13: -asum: command not found
shasum mismatch, expect d2c94fe597eef41188e0b30fd194ea86a26daa2c4694a75c5dea35d2c042f0ae, got Checking:
rm: cannot remove '/home/X/.nave/src/21.0.0.tgz': No such file or directory
Couldn't fetch 21.0.0