Add semi for ts function declarations without body (#1911)

Fixes #1891

src/printer.js

@@ -383,6 +383,9 @@ function genericPrintNoParens(path, options, print, args) {
         parts.push("declare ");
       }
       parts.push(printFunctionDeclaration(path, print, options));
+      if (n.type === "TSNamespaceFunctionDeclaration" && !n.body) {
+        parts.push(semi);
+      }
       return concat(parts);
     case "ArrowFunctionExpression": {
       if (n.async) {

tests/typescript/compiler/__snapshots__/jsfmt.spec.js.snap

@@ -772,7 +772,7 @@ namespace glo_M1_public {
 }
 
 declare module "glo_M2_public" {
-  export function f1()
+  export function f1();
   export class c1 {}
   export var v1: { new (): c1 };
   export var v2: c1;

tests/typescript_method/__snapshots__/jsfmt.spec.js.snap

@@ -1,5 +1,18 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`semi.js 1`] = `
+declare module 'foo' {
+  function foo(namespace: string): void;
+  function bar(namespace: string): void;
+}
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+declare module "foo" {
+  function foo(namespace: string): void;
+  function bar(namespace: string): void;
+}
+
+`;
+
 exports[`type_literal_optional_method.ts 1`] = `
 var v: { e?(): number };
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

tests/typescript_method/semi.js

@@ -0,0 +1,4 @@
+declare module 'foo' {
+  function foo(namespace: string): void;
+  function bar(namespace: string): void;
+}