fix some comments (#5194)

Signed-off-by: cui fliter <imcusg@gmail.com>

client/cache/error_code.go

@@ -185,7 +185,7 @@ When you try to use SSDB cache, it failed. There are many cases:
 `)
 
 var SsdbBadResponse = berror.DefineCode(5002007, moduleName, "SsdbBadResponse", `
-The reponse from SSDB server is invalid. 
+The response from SSDB server is invalid. 
 Usually it indicates something wrong on server side.
 `)
 

client/cache/file.go

@@ -122,7 +122,7 @@ func (fc *FileCache) Init() error {
 	return nil
 }
 
-// getCachedFilename returns an md5 encoded file name.
+// getCacheFileName returns a md5 encoded file name.
 func (fc *FileCache) getCacheFileName(key string) (string, error) {
 	m := md5.New()
 	_, _ = io.WriteString(m, key)