make geo.(lon|lat)axis.tick0 dflt=0

- so that it matches the current behavior (i.e. where
  tick0 didn't do a thing)

Author: etpinard

src/plots/geo/layout/defaults.js

@@ -60,7 +60,7 @@ function handleGeoDefaults(geoLayoutIn, geoLayoutOut, coerce) {
 
         var range = coerce(axisName + '.range', rangeDflt);
 
-        coerce(axisName + '.tick0', range[0]);
+        coerce(axisName + '.tick0');
         coerce(axisName + '.dtick', dtickDflt);
 
         show = coerce(axisName + '.showgrid');

src/plots/geo/layout/layout_attributes.js

@@ -35,6 +35,7 @@ var geoAxesAttrs = {
     tick0: {
         valType: 'number',
         role: 'info',
+        dflt: 0,
         description: [
             'Sets the graticule\'s starting tick longitude/latitude.'
         ].join(' ')

test/image/baselines/geo_stereographic.png

@@ -73,7 +73,6 @@
             "lataxis": {
                 "showgrid": true,
                 "range": [ -75, 85 ],
-                "tick0": 0,
                 "gridwidth": 2,
                 "gridcolor": "black"
             }

test/image/mocks/geo_kavrayskiy7.json

@@ -268,8 +268,8 @@ describe('Test Geo layout defaults', function() {
 
                 expect(layoutOut.geo.lonaxis.range).toEqual(dfltLonaxisRange);
                 expect(layoutOut.geo.lataxis.range).toEqual(dfltLataxisRange);
-                expect(layoutOut.geo.lonaxis.tick0).toEqual(dfltLonaxisRange[0]);
-                expect(layoutOut.geo.lataxis.tick0).toEqual(dfltLataxisRange[0]);
+                expect(layoutOut.geo.lonaxis.tick0).toEqual(0);
+                expect(layoutOut.geo.lataxis.tick0).toEqual(0);
             });
 
             it('custom case for ' + s, function() {
@@ -284,8 +284,8 @@ describe('Test Geo layout defaults', function() {
 
                 expect(layoutOut.geo.lonaxis.range).toEqual(customLonaxisRange);
                 expect(layoutOut.geo.lataxis.range).toEqual(customLataxisRange);
-                expect(layoutOut.geo.lonaxis.tick0).toEqual(customLonaxisRange[0]);
-                expect(layoutOut.geo.lataxis.tick0).toEqual(customLataxisRange[0]);
+                expect(layoutOut.geo.lonaxis.tick0).toEqual(0);
+                expect(layoutOut.geo.lataxis.tick0).toEqual(0);
             });
         });
     });