fix: the body of switch statement is a block scope (#67)

index.js

@@ -7,7 +7,8 @@ function isScope(node) {
   return node.type === 'FunctionExpression' || node.type === 'FunctionDeclaration' || node.type === 'ArrowFunctionExpression' || node.type === 'Program';
 }
 function isBlockScope(node) {
-  return node.type === 'BlockStatement' || isScope(node);
+  // The body of switch statement is a block.
+  return node.type === 'BlockStatement' || node.type === 'SwitchStatement' || isScope(node);
 }
 
 function declaresArguments(node) {

test/fixtures/switch-statement.js

@@ -0,0 +1,6 @@
+switch (3) {
+  case 3:
+    let a;
+}
+
+a;

test/index.js

@@ -138,6 +138,9 @@ test('return_hash.js - named argument / parameter', function () {
 test('right_hand.js - globals on the right-hand of assignment', function () {
   assert.deepEqual(detect(read('right_hand.js')).map(nameOf), [ 'exports', '__dirname', '__filename' ].sort());
 });
+test('switch-statement.js - id in outer scope of switch is a global', function () {
+  assert.deepEqual(detect(read('switch-statement.js')).map(nameOf), ['a']);
+});
 test('try_catch.js - the exception in a try catch block is a local', function () {
   assert.deepEqual(detect(read('try_catch.js')), []);
 });