fix scalar definition into exp list (related to #532)

Author: ichiriac

src/parser.js

@@ -231,6 +231,11 @@ const parser = function (lexer, ast) {
         this.tok.T_FILE,
         this.tok.T_DIR,
         this.tok.T_NS_C,
+        '"',
+        'b"',
+        'B"',
+        "-",
+        this.tok.T_NS_SEPARATOR,
       ].map(mapIt)
     ),
   };

src/parser/expr.js

@@ -359,7 +359,7 @@ module.exports = {
         let value = null;
         let key = null;
         result = this.node("yield");
-        if (this.next().is("EXPR") || this.is("SCALAR")) {
+        if (this.next().is("EXPR")) {
           // reads the yield return value
           value = this.read_expr();
           if (this.token === this.tok.T_DOUBLE_ARROW) {