Fixed ToString() of Flow and Revolution to match other classes.

Author: angularsen

Src/UnitsNet/Flow.cs

@@ -144,7 +144,7 @@ public override int GetHashCode()
 
 		public override string ToString()
 		{
-			return CubicMeterPerSecond + " " + UnitSystem.Create(CultureInfo.CurrentCulture).GetDefaultAbbreviation(Unit.CubicMeterPerSecond);
+            return string.Format("≈{0:0.##} {1}", CubicMeterPerSecond, UnitSystem.Create().GetDefaultAbbreviation(Unit.CubicMeterPerSecond));
 		}
 	}
 }

Src/UnitsNet/Revolution.cs

@@ -144,7 +144,7 @@ public override int GetHashCode()
 
 		public override string ToString()
 		{
-			return RevolutionsPerSecond + " " + UnitSystem.Create(CultureInfo.CurrentCulture).GetDefaultAbbreviation(Unit.RevolutionsPerSecond);
+            return string.Format("≈{0:0.##} {1}", RevolutionsPerSecond, UnitSystem.Create().GetDefaultAbbreviation(Unit.RevolutionsPerSecond));
 		}
 	}
 }