Set Sonatype OSS as the parent artifact. (#1)

Author: swalkowski

functions-framework-api/pom.xml

@@ -15,6 +15,13 @@
 -->
 <project>
   <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.sonatype.oss</groupId>
+    <artifactId>oss-parent</artifactId>
+    <version>9</version>
+  </parent>
+
   <groupId>com.google.cloud</groupId>
   <artifactId>functions-framework-api</artifactId>
   <version>1.0.0-alpha-1</version>