fix: one more small formatting glitch

Author: gvwilson

src/plots/cartesian/layout_attributes.js

@@ -334,7 +334,7 @@ module.exports = {
         description: [
             'If *normal*, the range is computed in relation to the extrema',
             'of the input data.',
-            'If *tozero*`, the range extends to 0,',
+            'If *tozero*, the range extends to 0,',
             'regardless of the input data',
             'If *nonnegative*, the range is non-negative,',
             'regardless of the input data.',

src/plots/polar/layout_attributes.js

@@ -73,7 +73,7 @@ var radialAxisAttrs = {
         dflt: 'tozero',
         editType: 'calc',
         description: [
-            'If *tozero*`, the range extends to 0,',
+            'If *tozero*, the range extends to 0,',
             'regardless of the input data',
             'If *nonnegative*, the range is non-negative,',
             'regardless of the input data.',

src/traces/carpet/axis_attributes.js

@@ -86,7 +86,7 @@ module.exports = {
         description: [
             'If *normal*, the range is computed in relation to the extrema',
             'of the input data.',
-            'If *tozero*`, the range extends to 0,',
+            'If *tozero*, the range extends to 0,',
             'regardless of the input data',
             'If *nonnegative*, the range is non-negative,',
             'regardless of the input data.'