Fix mouseover events on imagery layer bubbles

This is just a minor thing that doesn't usually alter visible behaviour.

The mouseover and mouseout events would fire when moving between child
elements of the svg group which was unnecessary.

modules/svg/mapillary_images.js

@@ -164,8 +164,8 @@ export function svgMapillaryImages(projection, context, dispatch) {
         var groupsEnter = groups.enter()
             .append('g')
             .attr('class', 'viewfield-group')
-            .on('mouseover', mouseover)
-            .on('mouseout', mouseout)
+            .on('mouseenter', mouseover)
+            .on('mouseleave', mouseout)
             .on('click', click);
 
         groupsEnter

modules/svg/openstreetcam_images.js

@@ -147,8 +147,8 @@ export function svgOpenstreetcamImages(projection, context, dispatch) {
         var groupsEnter = groups.enter()
             .append('g')
             .attr('class', 'viewfield-group')
-            .on('mouseover', mouseover)
-            .on('mouseout', mouseout)
+            .on('mouseenter', mouseover)
+            .on('mouseleave', mouseout)
             .on('click', click);
 
         groupsEnter

modules/svg/streetside.js

@@ -209,8 +209,8 @@ export function svgStreetside(projection, context, dispatch) {
         var groupsEnter = groups.enter()
             .append('g')
             .attr('class', 'viewfield-group')
-            .on('mouseover', mouseover)
-            .on('mouseout', mouseout)
+            .on('mouseenter', mouseover)
+            .on('mouseleave', mouseout)
             .on('click', click);
 
         groupsEnter