add skip-ensure flag to avoid import cycle (#140)

For mocks generated outside of the tested package with tests lives inside the same package as the tested code (i.e. pkg_test not used) --skip-ensure suppresses import of the source pkg

https://github.com/matryer/moq/issues/139

fix typo in readme

README.md

@@ -33,6 +33,9 @@ moq [flags] source-dir interface [interface2 [interface3 [...]]]
     	package name (default will infer)
   -stub
     	return zero values when no mock implementation is provided, do not panic
+  -skip-ensure
+		suppress mock implementation check, avoid import cycle if mocks generated outside of the tested package
+
 Specifying an alias for the mock is also supported with the format 'interface:alias'
 Ex: moq -pkg different . MyInterface:MyMock
 ```