address comment

src/table_properties.rs

+// Copyright 2017 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 use crocksdb_ffi::{self, DBTablePropertiesCollection, ptr_to_string};
 use std::collections::HashMap;
 use std::slice;

src/table_properties_collector.rs

+// Copyright 2017 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 use crocksdb_ffi::{self, DBEntryType, DBTablePropertiesCollectorContext};
 use libc::{c_void, c_char, c_int, uint8_t, uint64_t, size_t};
 use std::collections::HashMap;
@@ -7,7 +20,7 @@ use std::slice;
 /// `TablePropertiesCollector` provides the mechanism for users to collect
 /// their own properties that they are interested in. This class is essentially
 /// a collection of callback functions that will be invoked during table
-/// building. It is construced with TablePropertiesCollectorFactory. The methods
+/// building. It is constructed with TablePropertiesCollectorFactory. The methods
 /// don't need to be thread-safe, as we will create exactly one
 /// TablePropertiesCollector object per table and then call it sequentially
 pub trait TablePropertiesCollector {

src/table_properties_collector_factory.rs

+// Copyright 2017 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
 use crocksdb_ffi::DBTablePropertiesCollectorFactoryContext;
 use libc::{c_void, c_char, uint32_t};
 use table_properties_collector::{TablePropertiesCollector, new_table_properties_collector_context};