link fullLayout.separators to ax._separators

- to avoid confusion as separators isn't an axis attribute

Author: etpinard

src/plots/cartesian/axes.js

@@ -1343,7 +1343,7 @@ function numFormat(v, ax, fmtoverride, hover) {
             if(dp) v = v.substr(0, dp + tickRound).replace(/\.?0+$/, '');
         }
         // insert appropriate decimal point and thousands separator
-        v = Lib.numSeparate(v, ax.separators, separatethousands);
+        v = Lib.numSeparate(v, ax._separators, separatethousands);
     }
 
     // add exponent

src/plots/cartesian/set_convert.js

@@ -419,7 +419,7 @@ module.exports = function setConvert(ax, fullLayout) {
 
     // copy ref to fullLayout.separators so that
     // methods in Axes can use it w/o having to pass fullLayout
-    ax.separators = fullLayout.separators;
+    ax._separators = fullLayout.separators;
 
     // and for bar charts and box plots: reset forced minimum tick spacing
     delete ax._minDtick;