AC_PID: minor format fix

libraries/AC_PID/AC_P_2D.h

@@ -60,6 +60,6 @@ private:
     // internal variables
     float _dt;          // time step in seconds
     Vector2f _error;    // time step in seconds
-    float _error_max; // error limit in positive direction
+    float _error_max;   // error limit in positive direction
     float _D1_max;      // maximum first derivative of output
 };