Cleanup log messaging

This change corrects a few logging issues:

 * Standardized formatting errors with '%v'.
 * Standardized failure warning word usage.
 * Corrected an instance of using the standard log library when
   the gitea log library should be used instead.

routers/repo/view.go

@@ -6,10 +6,12 @@ package repo
 
 import (
 	"bytes"
+	"encoding/base64"
 	"fmt"
 	gotemplate "html/template"
 	"io/ioutil"
 	"path"
+	"strconv"
 	"strings"
 
 	"code.gitea.io/git"
@@ -22,9 +24,7 @@ import (
 	"code.gitea.io/gitea/modules/markdown"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/templates"
-	"encoding/base64"
 	"github.com/Unknwon/paginater"
-	"strconv"
 )
 
 const (
@@ -193,7 +193,7 @@ func renderFile(ctx *context.Context, entry *git.TreeEntry, treeLink, rawLink st
 			var fileContent string
 			if content, err := templates.ToUTF8WithErr(buf); err != nil {
 				if err != nil {
-					log.Error(4, "ToUTF8WithErr: %s", err)
+					log.Error(4, "ToUTF8WithErr: %v", err)
 				}
 				fileContent = string(buf)
 			} else {