message: fix literal strings
diff: @@ -191,7 +191,7 @@ function parseSyncTex(pdfsyncBody: string) : PdfSyncObject {
  match = line.match(verticalBlockPattern)
  if (match) {
  if (currentPage === undefined || currentElement === undefined) {
  - throw new SyncTexJsError('Error: parse error at line ${i}. A new V block is not allowed here.')
  + throw new SyncTexJsError(`Error: parse error at line ${i}. A new V block is not allowed here.`)
  }
  const s1 = [Number(match[3]) / unit, Number(match[4]) / unit]
  const s2 = [Number(match[5]) / unit, Number(match[6]) / unit]
  @@ -228,7 +228,7 @@ function parseSyncTex(pdfsyncBody: string) : PdfSyncObject {
  match = line.match(horizontalBlockPattern)
  if (match) {
  if (currentPage === undefined || currentElement === undefined) {
  - throw new SyncTexJsError('Error: parse error at line ${i}. A new H block is not allowed here.')
  + throw new SyncTexJsError(`Error: parse error at line ${i}. A new H block is not allowed here.`)
  }
  const s1 = [Number(match[3]) / unit, Number(match[4]) / unit]
  const s2 = [Number(match[5]) / unit, Number(match[6]) / unit]
  @@ -265,7 +265,7 @@ function parseSyncTex(pdfsyncBody: string) : PdfSyncObject {
  match = line.match(elementBlockPattern)
  if (match) {
  if (currentPage === undefined || currentElement === undefined || !isBlock(currentElement)) {
  - throw new SyncTexJsError('Error: parse error at line ${i}. A new element is not allowed here.')
  + throw new SyncTexJsError(`Error: parse error at line ${i}. A new element is not allowed here.`)
  }
  const type = match[1]
  const fileNumber = parseInt(match[2])
  