Fix nvm_ls_remote() using decorated-grep

" export GREP_OPTIONS='-n' " in bashrc disrupts nvm_ls_remote().
so I have added "command" before "grep" to execute raw-grep

    $ nvm ls-remote
    200:v0.1.96	 52:v0.6.3	104:v0.8.14	 67:v0.7.1	    211:v0.2.2
    1:v0.5.1	 62:v0.6.8	205:v0.1.99	 77:v0.7.3	    111:v0.
    5:v0.5.2	 32:v0.6.13 ..................................