Update pom.xml

I was getting the following warnings:

```
[WARNING]
[WARNING] Plugin validation issues were detected in 4 plugin(s)
[WARNING]
[WARNING]  * se.bjurr.gitchangelog:git-changelog-maven-plugin:1.97.0
[WARNING]   Declared at location(s):
[WARNING]    * com.drw.risk:bloomberg_market_bridge:0.0.14-SNAPSHOT (pom.xml) @ line 296
[WARNING]   Used in module(s):
[WARNING]    * com.drw.risk:bloomberg_market_bridge:0.0.14-SNAPSHOT (pom.xml)
[WARNING]   Plugin issue(s):
[WARNING]    * Plugin should declare these Maven artifacts in `provided` scope: [org.apache.maven:maven-core:3.6.0, org.apache.maven:maven-model-builder:3.6.0, org.apache.maven:maven-model:3.6.0, org.apache.maven:maven-builder-support:3.6.0, org.apache.maven:maven-settings:3.6.0, org.apache.maven:maven-resolver-provider:3.6.0, org.apache.maven:maven-settings-builder:3.6.0, org.apache.maven:maven-repository-metadata:3.6.0, org.apache.maven:maven-artifact:3.6.0]
```

Hopefully this is an acceptable way to resolve them.

pom.xml

@@ -57,6 +57,7 @@
 			<groupId>org.apache.maven</groupId>
 			<artifactId>maven-core</artifactId>
 			<version>3.6.0</version>
+			<scope>provided</scope>
 		</dependency>
 		<dependency>
 			<groupId>org.apache.maven.plugin-tools</groupId>
@@ -159,4 +160,4 @@
 			</build>
 		</profile>
 	</profiles>
-</project>
+</project>