DATAJDBC-383 - preliminary fix for not using http for MyBatis DTDs.

Currently there seems to be now well maintained https resource for MyBatis DTDs.
We therefore use the tagged sources directly for now.

See also: https://github.com/mybatis/mybatis-3/issues/1559

src/test/resources/org/springframework/data/jdbc/mybatis/DummyEntityMapper.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE mapper
 		PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
-		"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
+		"https://raw.githubusercontent.com/mybatis/mybatis-3/mybatis-3.5.1/src/main/java/org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd">
 <mapper namespace="org.springframework.data.jdbc.mybatis.DummyEntityMapper">
 	<resultMap id="dummyEntityMap" type="DummyEntity">
 		<constructor>

src/test/resources/org/springframework/data/jdbc/mybatis/mapper/DummyEntityMapper.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8" ?>
 <!DOCTYPE mapper
 		PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
-		"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
+		"https://raw.githubusercontent.com/mybatis/mybatis-3/mybatis-3.5.1/src/main/java/org/apache/ibatis/builder/xml/mybatis-3-mapper.dtd">
 <mapper namespace="org.springframework.data.jdbc.mybatis.mapper.DummyEntityMapper">
 	<resultMap id="dummyEntityMap" type="DummyEntity">
 		<constructor>