Fix for Expression class: inner string can be single quoted

core/math/expression.cpp

@@ -896,6 +896,7 @@ Error Expression::_get_token(Token &r_token) {
 
 				return OK;
 			}
+			case '\'':
 			case '"': {
 				String str;
 				while (true) {
@@ -905,7 +906,8 @@ Error Expression::_get_token(Token &r_token) {
 						_set_error("Unterminated String");
 						r_token.type = TK_ERROR;
 						return ERR_PARSE_ERROR;
-					} else if (ch == '"') {
+					} else if (ch == cchar) {
+						// cchar contain a corresponding quote symbol
 						break;
 					} else if (ch == '\\') {
 						//escaped characters...