fix(plugin): properly replace paths on Windows

Fixes #106

Author: kisenka

lib/utils/replace-sprite-placeholder.js

@@ -1,5 +1,7 @@
 const escapeRegExpSpecialChars = require('escape-string-regexp');
 
+const isWindows = /^win/i.test(process.platform);
+
 /**
  * @param {string} content
  * @param {Object<string, string>} replacements
@@ -9,9 +11,10 @@ function replaceSpritePlaceholder(content, replacements) {
   let result = content;
   Object.keys(replacements)
     .map((subj) => {
+      const normalizedSubj = isWindows ? subj.replace(/\\/g, '\\\\') : subj;
       return {
         subj,
-        re: new RegExp(escapeRegExpSpecialChars(subj), 'g')
+        re: new RegExp(escapeRegExpSpecialChars(normalizedSubj), 'g')
       };
     })
     .forEach(({ subj, re }) => {