Fix Composer version check

I've seen this for a few versions of VVV that in both Ubuntu 12.04 and 14.04 the below line of code would always evaluate to false, and as such, always install Composer instead of checking for an update:
```bash
if [[ -n "$(composer --version | grep -q 'Composer version')" ]]; then
```

I propose using the following, which seems to evaluate more consistently:
```bash
if [[ -n "$(composer --version --no-ansi | grep 'Composer version')" ]]; then
```
Merge pull request #400 from thewebists/patch-1

Fix Composer version check