Fix invalid JSON caused by localized decimal mark

[WolfspiritM]

As mentioned in #123 TimeSpanConverter produced wrongly formatted (non JSON) floating point numbers on systems with comma (or any other decimal mark) instead of dot causing the Glimpse HUD not showing at all as $.getJson doesn't return without error.

The produced JSON on a system with comma as seperator before this PR looked like this:

...
{
    "id": "0233a1ec5c7c3f22a1e52540157799a2",
    "ordinal": 524,
    "types": ["after-action-invoked"],
    "payload": {
        "actionId": "2d93d149-adba-4fca-a038-4162a6b96558",
        "actionName": "Index",
        "actionControllerName": "Home",
        "actionInvokedEndTime": "2016-07-27T14:47:11.8773171Z",
        "actionInvokedDuration": 27,64,
        "actionInvokedOffset": 0,76
    },
    "context": {
        "id": "dcc911aba2e540788469117426011cb1",
        "type": "Request"
    }
}
...

After this PR the json will look like this:

...
{
    "id": "0233a1ec5c7c3f22a1e52540157799a2",
    "ordinal": 524,
    "types": ["after-action-invoked"],
    "payload": {
        "actionId": "2d93d149-adba-4fca-a038-4162a6b96558",
        "actionName": "Index",
        "actionControllerName": "Home",
        "actionInvokedEndTime": "2016-07-27T14:47:11.8773171Z",
        "actionInvokedDuration": 27.64,
        "actionInvokedOffset": 0.76
    },
    "context": {
        "id": "dcc911aba2e540788469117426011cb1",
        "type": "Request"
    }
}
...

[avanderhoorn]

Thanks for the PR!