[analyzer] Fix memory error bug category capitalization.

It was written as "Memory Error" in most places and as "Memory error" in a few
other places, however it is the latter that is more consistent with
other categories (such as "Logic error").

rdar://problem/31718115

Differential Revision: https://reviews.llvm.org/D32702

llvm-svn: 302016
diff --git a/clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp
index 21527d8..41999d2 100644
--- a/clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/NullabilityChecker.cpp
@@ -178,7 +178,7 @@
                  const MemRegion *Region, BugReporter &BR,
                  const Stmt *ValueExpr = nullptr) const {
     if (!BT)
-      BT.reset(new BugType(this, "Nullability", "Memory error"));
+      BT.reset(new BugType(this, "Nullability", categories::MemoryError));
 
     auto R = llvm::make_unique<BugReport>(*BT, Msg, N);
     if (Region) {