SystemMonitor: Move memory graph caption from KB to KiB

This changes the graph caption from KB to KiB, but it keeps just "K"
instead of "KiB" for all the numbers in columns in the table, since "K"
is fairly well-established as abbreviation of "KiB" (the SI prefix is
lower-case), and space is at a premium here.

Applications/SystemMonitor/main.cpp

@@ -559,7 +559,7 @@ NonnullRefPtr<GUI::Widget> build_graphs_tab()
         memory_graph.set_text_color(Color::Cyan);
         memory_graph.set_graph_color(Color::from_rgb(0x00bbbb));
         memory_graph.text_formatter = [](int value, int max) {
-            return String::format("%d / %d KB", value, max);
+            return String::format("%d / %d KiB", value, max);
         };
 
         self.add<MemoryStatsWidget>(memory_graph);