Ensure that the mph values are also formatted

Without this fix, the mph values had lots of decimal points.
Note that we might not actually need to `parseFloat`, multiplying with numeric
strings seems to work fine at least in chrome.

```
ic.getKmph(metersPerSecond)
"10.80"
KM_TO_MILES  * ic.getKmph(metersPerSecond)
6.7108068
KM_TO_MILES  * 10.80
6.710806

KM_TO_MILES * "3.1"
1.9262501
```

But I presumably made the change for a reason, so let's be consistent throughout and change later if needed
98af95d

www/js/config/imperial.js

@@ -30,7 +30,7 @@ angular.module('emission.config.imperial', ['emission.plugin.logger'])
     };
 
     ic.getMph = function(metersPerSecond) {
-        return (KM_TO_MILES * ic.getKmph(metersPerSecond));
+        return (KM_TO_MILES * Number.parseFloat(ic.getKmph(metersPerSecond))).toFixed(2);
     };
 
     ic.getFormattedDistance = USE_IMPERIAL? ic.getFormattedDistanceInMiles : ic.getFormattedDistanceInKm;