chore: maven-compiler-plugin固定版本以去除警告，并增加构建稳定性

```
[WARNING]
[WARNING] Some problems were encountered while building the effective model for com.github.pagehelper:pagehelper:jar:6.0.0
[WARNING] 'build.plugins.plugin.version' for org.apache.maven.plugins:maven-compiler-plugin is missing. @ line 223, column 29
[WARNING]
[WARNING] It is highly recommended to fix these problems because they threaten the stability of your build.
[WARNING]
[WARNING] For this reason, future Maven versions might no longer support building such malformed projects.
```

应使用pluginManagement来固定版本，且可减少重复配置

pom.xml

@@ -193,7 +193,20 @@
         </dependency>
         -->
     </dependencies>
-
+    <build>
+        <pluginManagement>
+            <plugins>
+                <plugin>
+                    <artifactId>maven-compiler-plugin</artifactId>
+                    <version>3.11.0</version>
+                    <configuration>
+                        <source>8</source>
+                        <target>8</target>
+                    </configuration>
+                </plugin>
+            </plugins>
+        </pluginManagement>
+    </build>
     <profiles>
         <profile>
             <id>dev</id>
@@ -205,10 +218,6 @@
                     <!--Compiler-->
                     <plugin>
                         <artifactId>maven-compiler-plugin</artifactId>
-                        <configuration>
-                            <source>8</source>
-                            <target>8</target>
-                        </configuration>
                     </plugin>
                     <plugin>
                         <groupId>org.apache.maven.plugins</groupId>
@@ -230,10 +239,6 @@
                     <!--Compiler-->
                     <plugin>
                         <artifactId>maven-compiler-plugin</artifactId>
-                        <configuration>
-                            <source>8</source>
-                            <target>8</target>
-                        </configuration>
                     </plugin>
                     <!-- Source -->
                     <plugin>