Unset $GOMAXPROCS during tests (#4)

In order to test the `maxprocs` package, we need to control the value of
`$GOMAXPROCS`. Unfortunately, Travis sets `$GOMAXPROCS` in every
container.

To work around this, use `TestMain` to unset `$GOMAXPROCS` for the
`maxprocs` package tests.

Makefile

@@ -17,7 +17,7 @@ dependencies:
 	glide install
 ifdef SHOULD_LINT
 	@echo "Installing golint..."
-	go install ./vendor/github.com/golang/lint/golint
+	go get -u github.com/golang/lint/golint
 else
 	@echo "Not installing golint, since we don't expect to lint on" $(GO_VERSION)
 endif

glide.yaml

@@ -1,7 +1,6 @@
 package: go.uber.org/automaxprocs
 import: []
 testImport:
-- package: github.com/golang/lint/golint
 - package: github.com/stretchr/testify
   version: ^1.1.4
   subpackages:

maxprocs/maxprocs_test.go

@@ -24,6 +24,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"log"
 	"os"
 	"strconv"
 	"testing"
@@ -141,3 +142,10 @@ func TestSet(t *testing.T) {
 		assert.Equal(t, 42, currentMaxProcs(), "should change GOMAXPROCS to match quota")
 	})
 }
+
+func TestMain(m *testing.M) {
+	if err := os.Unsetenv(_maxProcsKey); err != nil {
+		log.Fatalf("Couldn't clear %s: %v\n", _maxProcsKey, err)
+	}
+	os.Exit(m.Run())
+}