Move .PHONY next to each target

It's clearer to keep target and it's .PHONY together. When reading
Makefile it's easier to see if target is phony or not (without jumping
back to first line and reading all of .PHONY dependencies). It's also
harder to forget remove/rename .PHONY dependency when target is changed
when they are together.

There is no official standard but make documentation[1] in .DEFAULT_GOAL
use multiple .PHONY:
> .PHONY: foo
> foo: ; @echo $@
>
> $(warning default goal is $(.DEFAULT_GOAL))
>
> # Reset the default goal.
> .DEFAULT_GOAL :=
>
> .PHONY: bar
> bar: ; @echo $@

PR: #369
[1]: https://www.gnu.org/software/make/manual/html_node/Special-Variables.html

Signed-off-by: Wojciech Szarański <wojciech.szaranski@gmail.com>

Makefile

@@ -1,21 +1,26 @@
-.PHONY: test testrace int ci clean help
+.PHONY: test
 test: ### Run unit tests
 	go test ./...
 
+.PHONY: testrace
 testrace: ### Run unit tests with race detector
 	go test -race ./...
 
+.PHONY: int
 int: ### Run integration tests (doesn't download redis server)
 	${MAKE} -C integration int
 
+.PHONY: ci
 ci: ### Run full tests suite (including download and compilation of proper redis server)
 	${MAKE} test
 	${MAKE} -C integration redis_src/redis-server int
 	${MAKE} testrace
 
+.PHONY: clean
 clean: ### Clean integration test files and remove compiled redis from integration/redis_src
 	${MAKE} -C integration clean
 
+.PHONY: help
 help:
 ifeq ($(UNAME), Linux)
 	@grep -P '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | \