Fix some typographical errors in comments

Fixes: #153
Applied from: #153

src/station_base.h

@@ -72,7 +72,7 @@ public:
 	/**
 	 * Invalid constructor. This can't be called as a FlowStat must not be
 	 * empty. However, the constructor must be defined and reachable for
-	 * FlwoStat to be used in a std::map.
+	 * FlowStat to be used in a std::map.
 	 */
 	inline FlowStat() {NOT_REACHED();}