fixed nvm_version result when multiple versions match the given pattern

since commit b6469ee186926fcdc3d85f5b118742960878692d ("Preventing an extra leading newline.") with multilple v0.10.* installed  I got the following error:

```
$ nvm use 0.10
bash: [: v0.10.25: binary operator expected
bash: [: v0.10.25: binary operator expected
v0.10.25
v0.10.26 version is not installed yet
```
instead of the expected:
```
$ nvm use 0.10
Now using node v0.10.26
```

the provided patch fixes it for me. 
(It's my first pull request on github so please bear with me :)