define err with the same code style (#3199)

association.go

@@ -170,7 +170,7 @@ func (association *Association) Replace(values ...interface{}) error {
 			if column, values := schema.ToQueryValues(rel.JoinTable.Table, joinPrimaryKeys, pvs); len(values) > 0 {
 				tx.Where(clause.IN{Column: column, Values: values})
 			} else {
-				return ErrorPrimaryKeyRequired
+				return ErrPrimaryKeyRequired
 			}
 
 			_, rvs := schema.GetIdentityFieldValuesMapFromValues(values, relPrimaryFields)

errors.go

@@ -15,10 +15,10 @@ var (
 	ErrMissingWhereClause = errors.New("WHERE conditions required")
 	// ErrUnsupportedRelation unsupported relations
 	ErrUnsupportedRelation = errors.New("unsupported relations")
-	// ErrorPrimaryKeyRequired primary keys required
+	// ErrPrimaryKeyRequired primary keys required
-	ErrorPrimaryKeyRequired = errors.New("primary key required")
+	ErrPrimaryKeyRequired = errors.New("primary key required")
-	// ErrorModelValueRequired model value required
+	// ErrModelValueRequired model value required
-	ErrorModelValueRequired = errors.New("model value required")
+	ErrModelValueRequired = errors.New("model value required")
 	// ErrUnsupportedDriver unsupported driver
 	ErrUnsupportedDriver = errors.New("unsupported driver")
 	// ErrRegistered registered

finisher_api.go

@@ -325,7 +325,7 @@ func (db *DB) Pluck(column string, dest interface{}) (tx *DB) {
 			}
 		}
 	} else if tx.Statement.Table == "" {
-		tx.AddError(ErrorModelValueRequired)
+		tx.AddError(ErrModelValueRequired)
 	}
 
 	fields := strings.FieldsFunc(column, utils.IsChar)

statement.go

@@ -96,7 +96,7 @@ func (stmt *Statement) QuoteTo(writer clause.Writer, field interface{}) {
 
 		if v.Name == clause.PrimaryKey {
 			if stmt.Schema == nil {
-				stmt.DB.AddError(ErrorModelValueRequired)
+				stmt.DB.AddError(ErrModelValueRequired)
 			} else if stmt.Schema.PrioritizedPrimaryField != nil {
 				stmt.DB.Dialector.QuoteTo(writer, stmt.Schema.PrioritizedPrimaryField.DBName)
 			} else if len(stmt.Schema.DBNames) > 0 {