Fix indentation in code examples.

Fixes the indentation to 4 characters in all code examples in *.adoc files.

Original pull request #1948

src/main/antora/modules/ROOT/pages/jdbc/transactions.adoc

@@ -50,6 +50,7 @@ public class UserManagementImpl implements UserManagement {
             user.addRole(role);
             userRepository.save(user);
         }
+    }
 }
 ----
 

src/main/antora/modules/ROOT/pages/r2dbc/getting-started.adoc

@@ -100,10 +100,11 @@ Next, you need to create a table structure in your database, as follows:
 
 [source,sql]
 ----
-CREATE TABLE person
-  (id VARCHAR(255) PRIMARY KEY,
+CREATE TABLE person(
+    id VARCHAR(255) PRIMARY KEY,
     name VARCHAR(255),
-   age INT);
+    age INT
+);
 ----
 
 You also need a main application to run, as follows:
@@ -117,10 +118,11 @@ When you run the main program, the preceding examples produce output similar to
 
 [source]
 ----
-2018-11-28 10:47:03,893 DEBUG amework.core.r2dbc.DefaultDatabaseClient: 310 - Executing SQL statement [CREATE TABLE person
-  (id VARCHAR(255) PRIMARY KEY,
+2018-11-28 10:47:03,893 DEBUG amework.core.r2dbc.DefaultDatabaseClient: 310 - Executing SQL statement [CREATE TABLE person(
+     id VARCHAR(255) PRIMARY KEY,
      name VARCHAR(255),
-   age INT)]
+     age INT
+ )]
 2018-11-28 10:47:04,074 DEBUG amework.core.r2dbc.DefaultDatabaseClient: 908 - Executing SQL statement [INSERT INTO person (id, name, age) VALUES($1, $2, $3)]
 2018-11-28 10:47:04,092 DEBUG amework.core.r2dbc.DefaultDatabaseClient: 575 - Executing SQL statement [SELECT id, name, age FROM person]
 2018-11-28 10:47:04,436  INFO        org.spring.r2dbc.example.R2dbcApp:  43 - Person [id='joe', name='Joe', age=34]

src/main/antora/modules/ROOT/pages/r2dbc/mapping.adoc

@@ -199,7 +199,7 @@ The following example of a Spring Converter implementation converts from a `Row`
 [source,java]
 ----
 @ReadingConverter
- public class PersonReadConverter implements Converter<Row, Person> {
+public class PersonReadConverter implements Converter<Row, Person> {
 
     public Person convert(Row source) {
         Person p = new Person(source.get("id", String.class),source.get("name", String.class));