make: use yarn for installation of dependencies

backend/Makefile

@@ -4,7 +4,7 @@ test:
 
 .PHONY: install
 install:
-	npm install --quiet --no-spin
+	yarn
 	$(MAKE) compile-frontent
 
 # I'm not sure this is the best idea, let's see how this works out for us

circle.yml

@@ -2,7 +2,7 @@
 machine:
   post:
       - pip install --upgrade docker-compose==1.8.0
-      - npm install -g triton
+      - npm install -g triton yarn
       - echo '{"url":"https://eu-ams-1.api.joyent.com","account":"'$SDC_ACCOUNT'","keyId":"c3:30:35:9b:85:48:73:44:31:cc:4b:2e:6a:00:16:e2","name":"eu-ams-1","curr":true}' | triton profile create -f -
 
   timezone:

frontend/Makefile

@@ -4,7 +4,7 @@ test:
 
 .PHONY: install
 install:
-	npm install --quiet --no-spin
+	yarn
 
 .PHONY: compile
 compile: install