Add terminating separator to avoid path escaping (#2288)

Author: denysop

android/app/src/main/java/com/microsoft/codepush/react/FileUtils.java

@@ -124,7 +124,7 @@ public static String readFileToString(String filePath) throws IOException {
     }
 
     private static String validateFileName(String fileName, File destinationFolder) throws IOException {
-        String destinationFolderCanonicalPath = destinationFolder.getCanonicalPath();
+        String destinationFolderCanonicalPath = destinationFolder.getCanonicalPath() + File.separator;
 
         File file = new File(destinationFolderCanonicalPath, fileName);
         String canonicalPath = file.getCanonicalPath();