Fix BuckRunner of IntelliJ plugin.

Summary: Should remove `process.destroy()` instead of `process.waitFor()`.

Test Plan: Build plugin.
diff --git a/plugin/src/com/facebook/buck/plugin/intellij/commands/BuckRunner.java b/plugin/src/com/facebook/buck/plugin/intellij/commands/BuckRunner.java
index 251e41a..616b684 100644
--- a/plugin/src/com/facebook/buck/plugin/intellij/commands/BuckRunner.java
+++ b/plugin/src/com/facebook/buck/plugin/intellij/commands/BuckRunner.java
@@ -109,7 +109,7 @@
       int exitCode;
       Future<String> stdoutFuture = readStream(process.getInputStream());
       Future<String> stderrFuture = readStream(process.getErrorStream());
-      process.destroy();
+      exitCode = process.waitFor();
       stdout = stdoutFuture.get();
       stderr = stderrFuture.get();
       return exitCode;