make sure hapi fhir base creates sources jar

In order to streamline build of android jar with dependencies all
dependencies should publish a sources jar also.

hapi-fhir-base/pom.xml

@@ -132,6 +132,20 @@
 	</dependencies>
 
 	<build>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-source-plugin</artifactId>
+				<executions>
+					<execution>
+						<id>attach-sources</id>
+						<goals>
+							<goal>jar</goal>
+						</goals>
+					</execution>
+				</executions>
+			</plugin>
+		</plugins>
 		<resources>
 			<resource>
 				<directory>src/main/resources</directory>