Revert "remove DoExpression generator"

This reverts commit 5cd8822888067d2615f620d1340df688d73108e4.

src/babel/generation/generators/expressions.js

@@ -22,6 +22,16 @@ export function UnaryExpression(node, print) {
   print.plain(node.argument);
 }
 
+/**
+ * Prints DoExpression, prints body.
+ */
+
+export function DoExpression(node, print) {
+  this.push("do");
+  this.space();
+  print.plain(node.body);
+}
+
 /**
  * Prints ParenthesizedExpression, prints expression.
  */