improve comments

Author: etpinard

src/traces/histogram/calc.js

@@ -292,6 +292,7 @@ function calcAllAutoBins(gd, trace, pa, mainData, _overlayEdgeCase) {
         }
 
         // TODO how does work with bingroup ????
+        // - https://github.com/plotly/plotly.js/issues/3881
         //
         // Edge case: single-valued histogram overlaying others
         // Use them all together to calculate the bin size for the single-valued one

test/jasmine/tests/histogram_test.js

@@ -378,7 +378,6 @@ describe('Test histogram', function() {
             ]);
         });
 
-        // TODO figure out what to do in this case!
         it('should be able to group histogram and histogram2d* traces together', function() {
             gd = {
                 data: [
@@ -447,7 +446,6 @@ describe('Test histogram', function() {
                     {bingroup: '1', type: 'histogram', y: [2, 3], xaxis: 'x2', yaxis: 'y2'},
                     // this one does not have to match either
                     // (it's a histogram2d* traces), but it can be grouped
-                    // TODO should this be just "bingroup"???
                     {xbingroup: '1', ybingroup: '1', type: 'histogram2d', x: [3, 4], y: [3, 4]}
                 ],
                 layout: {}