[clang-tidy] use bool literals (#881)

Found with modernize-use-bool-literals

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/parse.cpp

@@ -51,7 +51,7 @@ std::vector<Node> LoadAll(std::istream& input) {
   std::vector<Node> docs;
 
   Parser parser(input);
-  while (1) {
+  while (true) {
     NodeBuilder builder;
     if (!parser.HandleNextDocument(builder)) {
       break;