Require context in AttributionParser.Options

[LukasPaczos]

If context has not been passed as an AttributionParser option, it was going to crash when getting a translated string.

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object java.lang.ref.WeakReference.get()' on a null object reference
    at com.mapbox.mapboxsdk.attribution.AttributionParser.translateImproveThisMapAnchor(AttributionParser.java:146)
    at com.mapbox.mapboxsdk.attribution.AttributionParser.parseUrlSpan(AttributionParser.java:113)
    at com.mapbox.mapboxsdk.attribution.AttributionParser.parseAttributions(AttributionParser.java:98)
    at com.mapbox.mapboxsdk.attribution.AttributionParser.parse(AttributionParser.java:87)
    at com.mapbox.mapboxsdk.attribution.AttributionParser$Options.build(AttributionParser.java:302)
    at com.mapbox.mapboxsdk.snapshotter.MapSnapshotter.createAttributionString(MapSnapshotter.java:448)
    at com.mapbox.mapboxsdk.snapshotter.MapSnapshotter.createTextView(MapSnapshotter.java:429)
    at com.mapbox.mapboxsdk.snapshotter.MapSnapshotter.getAttributionMeasure(MapSnapshotter.java:365)
    at com.mapbox.mapboxsdk.snapshotter.MapSnapshotter.drawOverlay(MapSnapshotter.java:355)
    at com.mapbox.mapboxsdk.snapshotter.MapSnapshotter.addOverlay(MapSnapshotter.java:350)
    at com.mapbox.mapboxsdk.snapshotter.MapSnapshotter$1.run(MapSnapshotter.java:506)