Fixed SyntaxError with import hook, future imports and module docstring

Fixes #87.

docs/versionhistory.rst

@@ -3,6 +3,11 @@ Version history
 
 This library adheres to `Semantic Versioning 2.0 <https://semver.org/#semantic-versioning-200>`_.
 
+**UNRELEASED**
+
+- Fixed import errors when using the import hook and trying to import a module that has both a
+  module docstring and ``__future__`` imports in it
+
 **2.6.0** (2019-11-06)
 
 - Added a :pep:`302` import hook for annotating functions and classes with ``@typechecked``

tests/dummymodule.py

@@ -1,3 +1,4 @@
+"""Module docstring."""
 from __future__ import absolute_import
 from __future__ import division
 

typeguard/importhook.py

@@ -27,6 +27,8 @@ def visit_Module(self, node: ast.Module):
         for i, child in enumerate(node.body):
             if isinstance(child, ast.ImportFrom) and child.module == '__future__':
                 continue
+            elif isinstance(child, ast.Expr) and isinstance(child.value, ast.Str):
+                continue  # module docstring
             else:
                 node.body.insert(i, ast.Import(names=[ast.alias('typeguard', None)]))
                 break