Update tools (#492)

This bumps the tools we use during build and linting to latest
versions in hope of fixing an annoying warning I was often getting
during linting.

The warnings I was getting were for example:

WARN [runner] Can't run linter goanalysis_metalinter: ctrlflow: failed
prerequisites: [email protected]/otel/exporter/metric/stdout
[go.opentelemetry.io/otel/sdk/metric.test]

WARN [runner] Can't run linter goanalysis_metalinter: fact_purity:
failed prerequisites:
[email protected]/otel/internal/metric
[go.opentelemetry.io/otel/api/metric.test]

Author: krnowak

tools/go.mod

@@ -4,6 +4,6 @@ go 1.13
 
 require (
 	github.com/client9/misspell v0.3.4
-	github.com/golangci/golangci-lint v1.21.0
-	golang.org/x/tools v0.0.0-20191025174333-e96d959c4788
+	github.com/golangci/golangci-lint v1.23.6
+	golang.org/x/tools v0.0.0-20200220155224-947cbf191135
 )