SkPDF: fix typo s/ProcSets/ProcSet/

Change-Id: I7186307ddde1308d93eb4fe8463cf35a79e5dc27
Reviewed-on: https://skia-review.googlesource.com/c/164046
Auto-Submit: Hal Canary <halcanary@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
diff --git a/src/pdf/SkPDFDocument.cpp b/src/pdf/SkPDFDocument.cpp
index 31fba11..af57919 100644
--- a/src/pdf/SkPDFDocument.cpp
+++ b/src/pdf/SkPDFDocument.cpp
@@ -438,7 +438,7 @@
     for (const char* proc : kProcs) {
         procSet->appendName(proc);
     }
-    dict->insertObject("ProcSets", std::move(procSet));
+    dict->insertObject("ProcSet", std::move(procSet));
     return dict;
 }