fix(gatsby-plugin-mdx): Fix Safari 9 const syntax error (#15644)

1-800-jono · pieh · commit a82346365372 · 2019-07-12T12:45:44.000+02:00
`SyntaxError: Unexpected keyword 'const'. Const declarations are not supported in strict mode.`

Gatsby sites using mdx break in Safari 9 (possibly other older browsers) because it's using es6 `const`.
diff --git a/packages/gatsby-plugin-mdx/loaders/mdx-scopes.js b/packages/gatsby-plugin-mdx/loaders/mdx-scopes.js
@@ -12,7 +12,7 @@ module.exports = function() {
     files
       .map(
         (file, i) =>
-          `const scope_${i} = require('${slash(
+          `var scope_${i} = require('${slash(
             path.join(abs, file)
           )}').default;`
       )

Original file line number	Diff line number	Diff line change
`@@ -12,7 +12,7 @@ module.exports = function() {`
`12`	`12`	`files`
`13`	`13`	`.map(`
`14`	`14`	`(file, i) =>`
`15`		- `const scope_${i} = require('${slash(
	`15`	+ `var scope_${i} = require('${slash(
`16`	`16`	`path.join(abs, file)`
`17`	`17`	)}').default;`
`18`	`18`	`)`