Use HTTPS to link to Apache License [skip ci] (#488)

Author: nakamura-to

Diff for: LICENSE.txt

@@ -1,7 +1,7 @@
 
                                  Apache License
                            Version 2.0, January 2004
-                        http://www.apache.org/licenses/
+                        https://www.apache.org/licenses/
 
    TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
 
@@ -193,7 +193,7 @@
    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
+       https://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,