Autoloading of color extension not working

E.g.,

```
$ node bin/tex2svg --inline '\definecolor{red}{RGB}{255,0,0}\color{red}e^{i \pi} + 1 = 0'
```

returns with

```
TeX parse error: Undefined control sequence \definecolor
```

But 

```
$ node bin/tex2svg --inline '\require{color}\definecolor{red}{RGB}{255,0,0}\color{red}e^{i \pi} + 1 = 0'
```

works fine.
