Fix typo in documentation.

Fix https://github.com/bazelbuild/bazel/issues/12218.

PiperOrigin-RevId: 335598100
diff --git a/src/main/java/com/google/devtools/build/lib/runtime/LoadingPhaseThreadsOption.java b/src/main/java/com/google/devtools/build/lib/runtime/LoadingPhaseThreadsOption.java
index 85b2209..7340232 100644
--- a/src/main/java/com/google/devtools/build/lib/runtime/LoadingPhaseThreadsOption.java
+++ b/src/main/java/com/google/devtools/build/lib/runtime/LoadingPhaseThreadsOption.java
@@ -38,7 +38,7 @@
           "Number of parallel threads to use for the loading/analysis phase."
               + "Takes "
               + ResourceConverter.FLAG_SYNTAX
-              + ". \"auto\" sets a reasonable default based on"
+              + ". \"auto\" sets a reasonable default based on "
               + "host resources. Must be at least 1.")
   public int threads;