fix(markdown): do not keep increasing backslashes for dollar sign (#5358)

src/language-markdown/preprocess.js

@@ -46,7 +46,8 @@ function restoreUnescapedCharacter(ast, options) {
       : Object.assign({}, node, {
           value:
             node.value !== "*" &&
-            node.value !== "_" && // handle these two cases in printer
+            node.value !== "_" &&
+            node.value !== "$" && // handle these cases in printer
             isSingleCharRegex.test(node.value) &&
             node.position.end.offset - node.position.start.offset !==
               node.value.length

tests/markdown_math/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,24 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`dollar-sign.md - markdown-verify 1`] = `
+$
+
+\\$
+
+\\\\$
+
+\\\\\\$
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+\\$
+
+\\$
+
+\\\\\\$
+
+\\\\\\$
+
+`;
+
 exports[`empty-block.md - markdown-verify 1`] = `
 $$
 $$
@@ -107,7 +126,7 @@ $$
 
 ---
 
-\\\\$\\alpha\\$
+\\$\\alpha\\$
 
 ---
 

tests/markdown_math/dollar-sign.md

@@ -0,0 +1,7 @@
+$
+
+\$
+
+\\$
+
+\\\$

tests/markdown_spec/__snapshots__/jsfmt.spec.js.snap

@@ -3306,7 +3306,7 @@ exports[`example-284.md - markdown-verify 1`] = `
 exports[`example-285.md - markdown-verify 1`] = `
 \\!\\"\\#\\$\\%\\&\\'\\(\\)\\*\\+\\,\\-\\.\\/\\:\\;\\<\\=\\>\\?\\@\\[\\\\\\]\\^\\_\\\`\\{\\|\\}\\~
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-\\!\\"\\#\\\\$\\%\\&\\'\\(\\)\\*\\+\\,\\-\\.\\/\\:\\;\\<\\=\\>\\?\\@\\[\\\\\\]\\^\\_\\\`\\{\\|\\}\\~
+\\!\\"\\#\\$\\%\\&\\'\\(\\)\\*\\+\\,\\-\\.\\/\\:\\;\\<\\=\\>\\?\\@\\[\\\\\\]\\^\\_\\\`\\{\\|\\}\\~
 
 `;
 

tests/multiparser_js_markdown/__snapshots__/jsfmt.spec.js.snap

@@ -94,7 +94,7 @@ markdown\`
   - \\\\\\\`
   - \\\\ a
   - \\\\\\\\
-  - \\\\$
+  - \\$
   - \\u1234
 \`;