Rename make target `show-help` to `help` (#123)

* rename make target `show-help` to show_help

* rename show_help to help

{{ cookiecutter.repo_name }}/Makefile

@@ -86,7 +86,7 @@ test_environment:
 # Self Documenting Commands                                                     #
 #################################################################################
 
-.DEFAULT_GOAL := show-help
+.DEFAULT_GOAL := help
 
 # Inspired by <http://marmelab.com/blog/2016/02/29/auto-documented-makefile.html>
 # sed script explained:
@@ -103,8 +103,8 @@ test_environment:
 # 	* print line
 # Separate expressions are necessary because labels cannot be delimited by
 # semicolon; see <http://stackoverflow.com/a/11799865/1968>
-.PHONY: show-help
-show-help:
+.PHONY: help
+help:
 	@echo "$$(tput bold)Available rules:$$(tput sgr0)"
 	@echo
 	@sed -n -e "/^## / { \