[Releng] Fix path separator in build instructions
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a2cdad7..d1ca7e3 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -57,8 +57,8 @@
 run in `org.eclipse.statet`:
 
 ```
-mvn -f 3rdparty\bundle-recipes-pom.xml install
-mvn -f 3rdparty\pom.xml install
+mvn -f 3rdparty/bundle-recipes-pom.xml install
+mvn -f 3rdparty/pom.xml install
 ```
 
 ### StatET