logrus: use lower-case in comments and examples

doc.go

@@ -7,7 +7,7 @@ The simplest way to use Logrus is simply the package-level exported logger:
   package main
 
   import (
-    log "github.com/Sirupsen/logrus"
+    log "github.com/sirupsen/logrus"
   )
 
   func main() {
@@ -21,6 +21,6 @@ The simplest way to use Logrus is simply the package-level exported logger:
 Output:
   time="2015-09-07T08:48:33Z" level=info msg="A walrus appears" animal=walrus number=1 size=10
 
-For a full guide visit https://github.com/Sirupsen/logrus
+For a full guide visit https://github.com/sirupsen/logrus
 */
 package logrus