Fix golint errors

[whuang8]

Resolves #2

Errors Fixed

$ golint ./...
agent/agent.go:239:6: should omit values from range; this loop is equivalent to `for range ...`
agent/agent.go:261:6: should omit values from range; this loop is equivalent to `for range ...`
agent/banner/banner.go:143:3: struct field FavIconUrl should be FavIconURL
agent/banner/banner.go:188:9: if block ends with a return statement, so drop this else and outdent its block
agent/metrics/metrics.go:51:6: exported type MetricHandler should have comment or be unexported
agent/metrics/metrics.go:150:11: should omit 2nd value from range; this loop is equivalent to `for key := range ...`
agent/metrics/metrics.go:181:1: exported method MetricHandler.GetResponseCountMetricType should have comment or be unexported
agent/utils/utils.go:130:26: error strings should not be capitalized or end with punctuation or a newline
agent/utils/utils.go:141:26: error strings should not be capitalized or end with punctuation or a newline
agent/websockets/shim.go:256:1: exported function ShimBody should have comment or be unexported
testing/runlocal/main.go:60:1: exported function RunLocalProxy should have comment or be unexported

[whuang8]

This attribute is already being referenced by the updated name in the favIconLinkTemplate.

[ojarjur]

Thanks for the fixes!

I really appreciate you going out of your way to help improve the project's health.