Update bytes.pipe.ts (#89)

I've put an if check inside the format loop, checking for `hasOwnProperty.` Why:
https://palantir.github.io/tslint/rules/forin/

Another approach would have been to use `Object.keys(BytesPipe.formats).forEach` but there is no nice way of breaking out a forEach.

Author: samvloeberghs

src/math/bytes.pipe.ts

@@ -44,12 +44,14 @@ export class BytesPipe implements PipeTransform {
         }
 
         for (const key in BytesPipe.formats) {
-            const format = BytesPipe.formats[key];
-            if (bytes < format.max) {
+            if (BytesPipe.formats.hasOwnProperty(key)) {
+                const format = BytesPipe.formats[key];
+                if (bytes < format.max) {
 
-                const result = toDecimal(BytesPipe.calculateResult(format, bytes), decimal);
+                    const result = toDecimal(BytesPipe.calculateResult(format, bytes), decimal);
 
-                return BytesPipe.formatResult(result, key);
+                    return BytesPipe.formatResult(result, key);
+                }
             }
         }
     }
@@ -62,4 +64,4 @@ export class BytesPipe implements PipeTransform {
         const prev = format.prev ? BytesPipe.formats[format.prev] : undefined;
         return prev ? bytes / prev.max : bytes;
     }
-}
+}