Update CONTRIBUTING.md

fix typo

CONTRIBUTING.md

@@ -24,8 +24,8 @@ Some more instructions how to get started with bndtools development in Eclipse c
 - `./gradlew :gradle-plugins:publish` - Assembles and publishes the Bnd Gradle plugins into `dist/bundles`.
 - `./mvnw -Pdist deploy` - Assembles and publishes the Bnd Maven plugins into `dist/bundles`.
 
-Rebuilding: bnd is build with bnd. For that reason we rebuild and retest bnd with the build we just built.
-To do a full build-rebuilt cycle (like the github build), you can use the following command:
+Rebuilding: bnd is built with bnd. For that reason we rebuild and retest bnd with the build we just built.
+To do a full build-rebuild cycle (like the github build), you can use the following command:
 
 `./gradlew :build ; ./gradlew :gradle-plugins:build ; ./.github/scripts/rebuild-build.sh ; ./.github/scripts/rebuild-test.sh`