If prefix property ends with a hyphen, script changes src attrib to 'null'

[seajones]

Just using this code:

R.create({
    "prop": "width",
    "prefix": "src- src",
    "breakpoints": [320, 481, 641, 961, 1025, 1281]
});

Where R is within a closure, and alias to Response.

If the prefix property reads "src- src" (to make data-src320 and data-src-320 work for example) it works fine, but if the prefixes are swapped around thus:

R.create({
    "prop": "width",
    "prefix": "src src-",
    "breakpoints": [320, 481, 641, 961, 1025, 1281]
});

The src attributes, when changed by Response, are changed to read 'null'

Just a little thing, and mostly I'm posting this so users can spot this issue if it occurs for them.

[ryanve]

#25 is the same issue. Let's handle it there where there's more info.