Fix error in previous commit of 'ftruncate' to 'fallocate'.

Summary:
Fix error in previous commit of 'ftruncate' to 'fallocate'.

Test Plan:

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Task ID: #

Blame Rev:

util/env_test.cc

@@ -365,7 +365,7 @@ TEST(EnvPosixTest, PosixRandomRWFileTest) {
   unique_ptr<RandomRWFile> file;
   ASSERT_OK(env_->NewRandomRWFile(fname, &file, soptions));
   // If you run the unit test on tmpfs, then tmpfs might not
-  // support ftruncate. It is still better to trigger that
+  // support fallocate. It is still better to trigger that
   // code-path instead of eliminating it completely.
   file.get()->Allocate(0, 10*1024*1024);
   ASSERT_OK(file.get()->Write(100, Slice("Hello world")));