Bump Go versions for Travis, fix tests

Replace gometalinter with golangci-lint.

Fix system tests (wheezy is gone, replace with stretch).

Fix linter warnings.

Makefile

@@ -11,13 +11,10 @@ TESTS?=
 BINPATH?=$(GOPATH)/bin
 RUN_LONG_TESTS?=yes
 
-GO_1_10_AND_HIGHER=$(shell (printf '%s\n' go1.10 $(GOVERSION) | sort -cV >/dev/null 2>&1) && echo "yes")
-
 all: test bench check system-test
 
 prepare:
-	go get -u github.com/alecthomas/gometalinter
-	gometalinter --install
+	curl -sfL https://install.goreleaser.com/github.com/golangci/golangci-lint.sh | sh -s -- -b $(shell go env GOPATH)/bin v1.17.1
 
 dev:
 	go get -u github.com/golang/dep/...
@@ -25,11 +22,7 @@ dev:
 
 check: system/env
 ifeq ($(RUN_LONG_TESTS), yes)
-	if [ -x travis_wait ]; then \
-		travis_wait gometalinter --config=linter.json ./...; \
-	else \
-		gometalinter --config=linter.json ./...; \
-	fi
+	golangci-lint run
 	. system/env/bin/activate && flake8 --max-line-length=200 --exclude=system/env/ system/
 endif
 
@@ -51,14 +44,10 @@ ifeq ($(RUN_LONG_TESTS), yes)
 endif
 
 test:
-ifeq ($(GO_1_10_AND_HIGHER), yes)
 	go test -v ./... -gocheck.v=true -race -coverprofile=coverage.txt -covermode=atomic
-else
-	go test -v `go list ./... | grep -v vendor/` -gocheck.v=true
-endif
 
 bench:
-	go test -v ./deb -run=nothing -bench=. -benchmem 
+	go test -v ./deb -run=nothing -bench=. -benchmem
 
 mem.png: mem.dat mem.gp
 	gnuplot mem.gp