pom.xml: avoid warnings about defaulting to UTF-8
diff --git a/pom.xml b/pom.xml
index 6550075..f8f6683 100644
--- a/pom.xml
+++ b/pom.xml
@@ -9,6 +9,7 @@
   <packaging>pom</packaging>
 
   <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <tycho.version>1.0.0</tycho.version>
   </properties>
 
@@ -41,6 +42,17 @@
         </configuration>
       </plugin>
 
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-compiler-plugin</artifactId>
+        <version>3.7.0</version>
+        <configuration>
+          <encoding>UTF-8</encoding>
+          <source>1.8</source>
+          <target>1.8</target>
+        </configuration>
+      </plugin>
+
       <!-- Generate source bundles (exclude target so we don't enter
            an infinite loop for binary-only plugins, which have itself
            as the source). -->