Fix benchmark images

Author: Luc Dion

README.md

@@ -178,7 +178,7 @@ These results also mean that **PinLayout is by far faster than any layout framew
 
 <p align="center"> Tested on a iPhone 6 iOS 10.3.2</p>
 <p align="center">
-  <img src="docs/Benchmark/benchmark_iPhone6.png" alt="PinLayout Performance" width=600/>
+  <img src="docs/Benchmark/benchmark_iphone6.png" alt="PinLayout Performance" width=600/>
 </p>
 
 <br/>

docs/Benchmark.md

@@ -71,16 +71,16 @@ The table shows that **FlexLayout took 23 miliseconds** to render 100 UICollecti
 
 
 <p align="center">
-  <a href=""><img src="Benchmark/benchmark_iPhone5.png" alt="PinLayout Performance"/></a>
+  <a href=""><img src="Benchmark/benchmark_iphone5.png" alt="PinLayout Performance"/></a>
 
 <p align="center">
-  <a href=""><img src="Benchmark/benchmark_iPhone6.png" alt="PinLayout Performance"/></a>
+  <a href=""><img src="Benchmark/benchmark_iphone6.png" alt="PinLayout Performance"/></a>
 
 <p align="center">
-  <a href=""><img src="Benchmark/benchmark_iPhone6S.png" alt="PinLayout Performance"/></a>
+  <a href=""><img src="Benchmark/benchmark_iphone6S.png" alt="PinLayout Performance"/></a>
 
 <p align="center">
-  <a href=""><img src="Benchmark/benchmark_iPhone7.png" alt="PinLayout Performance"/></a>
+  <a href=""><img src="Benchmark/benchmark_iphone7.png" alt="PinLayout Performance"/></a>
 
 
 <br>