fix issue estools#371

simply adopted solution described by johnjbarton in issue estools#371

Author: fokushi-db

escodegen.js

@@ -967,7 +967,7 @@
             result = join(result, operator);
             result = [join(
                 result,
-                that.generateExpression(stmt.right, Precedence.Sequence, E_TTT)
+                that.generateExpression(stmt.right, Precedence.Assignment, E_TTT)
             ), ')'];
         });
         result.push(this.maybeBlock(stmt.body, flags));

test/compare-harmony/for-of-statement.expected.js

@@ -3,4 +3,6 @@ function test() {
     }
     for (let i of array) {
     }
+    for (let c of ('x', String('cat'))) {
+    }
 }

test/compare-harmony/for-of-statement.expected.min.js

@@ -1 +1 @@
-function test(){for(var i of array){}for(let i of array){}}
+function test(){for(var i of array){}for(let i of array){}for(let c of('x',String('cat'))){}}

test/compare-harmony/for-of-statement.js

@@ -4,4 +4,7 @@ function test() {
 
     for (let i of array) {
     }
+
+    for (let c of ('x', String('cat'))) {
+    }
 }