add rpdk.log to initially generated default .gitignore (#110)

https://github.com/aws-cloudformation/cloudformation-cli-java-plugin/blob/682214d782e20ee197ae2711bde06602d12a5d20/python/rpdk/java/data/java.gitignore#L20

https://github.com/aws-cloudformation/cloudformation-cli-go-plugin/blob/7b9fc8d8848ad2666298fbcf077c0f2d4d264a2b/python/rpdk/go/data/go.gitignore#L6

Author: PatMyron

python/rpdk/python/data/Python.gitignore

@@ -125,3 +125,5 @@ dmypy.json
 
 # contains credentials
 sam-tests/
+
+rpdk.log*