Update for Go 1.10 (#39)

* Add Go 1.10 to .travis.yml.
* Add quotes to Go versions in .travis.yml, because unquoted 1.10 is interpreted
as Go 1.1.
* Change .travis.yml references from 'tip' to 'master'. 'tip' is a legacy reference
coming from the days when the Go project used mercurial instead of git.

.travis.yml

@@ -1,11 +1,12 @@
 language: go
 go:
-- 1.7
-- 1.8
-- 1.9
-- tip
+- "1.7"
+- "1.8"
+- "1.9"
+- "1.10"
+- "master"
 matrix:
   allow_failures:
-      - go: tip
+      - go: "master"
 script:
   go test -v -race -cpu=1,2,4 -bench . -benchmem ./...

log/log_example_test.go

@@ -102,7 +102,7 @@ func ExampleFatal() {
 
 // This example uses command-line flags to demonstrate various outputs
 // depending on the chosen log level.
-func Example_LevelFlag() {
+func Example() {
 	setup()
 	debug := flag.Bool("debug", false, "sets log level to debug")