Replace domain.com with example.com (#434)

Because domain.com is an actual business, example.com should be used for example purposes.

README.md

@@ -88,7 +88,7 @@ r := mux.NewRouter()
 // Only matches if domain is "www.example.com".
 r.Host("www.example.com")
 // Matches a dynamic subdomain.
-r.Host("{subdomain:[a-z]+}.domain.com")
+r.Host("{subdomain:[a-z]+}.example.com")
 ```
 
 There are several other matchers that can be added. To match path prefixes:
@@ -238,13 +238,13 @@ This also works for host and query value variables:
 
 ```go
 r := mux.NewRouter()
-r.Host("{subdomain}.domain.com").
+r.Host("{subdomain}.example.com").
   Path("/articles/{category}/{id:[0-9]+}").
   Queries("filter", "{filter}").
   HandlerFunc(ArticleHandler).
   Name("article")
 
-// url.String() will be "http://news.domain.com/articles/technology/42?filter=gorilla"
+// url.String() will be "http://news.example.com/articles/technology/42?filter=gorilla"
 url, err := r.Get("article").URL("subdomain", "news",
                                  "category", "technology",
                                  "id", "42",
@@ -264,7 +264,7 @@ r.HeadersRegexp("Content-Type", "application/(text|json)")
 There's also a way to build only the URL host or path for a route: use the methods `URLHost()` or `URLPath()` instead. For the previous route, we would do:
 
 ```go
-// "http://news.domain.com/"
+// "http://news.example.com/"
 host, err := r.Get("article").URLHost("subdomain", "news")
 
 // "/articles/technology/42"
@@ -275,12 +275,12 @@ And if you use subrouters, host and path defined separately can be built as well
 
 ```go
 r := mux.NewRouter()
-s := r.Host("{subdomain}.domain.com").Subrouter()
+s := r.Host("{subdomain}.example.com").Subrouter()
 s.Path("/articles/{category}/{id:[0-9]+}").
   HandlerFunc(ArticleHandler).
   Name("article")
 
-// "http://news.domain.com/articles/technology/42"
+// "http://news.example.com/articles/technology/42"
 url, err := r.Get("article").URL("subdomain", "news",
                                  "category", "technology",
                                  "id", "42")