docs: Fix a non-valid html img tag in README.md

Cherry-pick to unstable.

Ref:

- Fix non-valid html5 img tag in README.md #3193
- The img tag in README.md is non-valid HTML5 #3192

README.md

@@ -1,4 +1,4 @@
-<img style="width: 200px; height: 200px;" src="https://raw.githubusercontent.com/cytoscape/cytoscape.js/unstable/documentation/img/cytoscape-logo.png" width="200" height="200"></img>
+<img style="width: 200px; height: 200px;" src="https://raw.githubusercontent.com/cytoscape/cytoscape.js/unstable/documentation/img/cytoscape-logo.png" width="200" height="200">
 
 [![GitHub repo](https://img.shields.io/badge/Repo-GitHub-yellow.svg)](https://github.com/cytoscape/cytoscape.js)
 [![Ask a question with Phind](https://img.shields.io/badge/Get%20help-Phind-yellow.svg)](https://www.phind.com/search?c=I%27m%20using%20the%20Cytoscape.js%20graph%20theory%20JS%20library.&q=How%20do%20I%20create%20a%20graph%20in%20my%20HTML%20page)
@@ -38,9 +38,9 @@ Learn more about the features of Cytoscape.js by reading [its documentation](htt
 
 The Tokyo railway stations network can be visualised with Cytoscape:
 
-<img style="width: 300px; height: 126px;" src="https://raw.githubusercontent.com/cytoscape/cytoscape.js/unstable/documentation/img/tokyo-big.png" width="300" height="126"></img>
+<img style="width: 300px; height: 126px;" src="https://raw.githubusercontent.com/cytoscape/cytoscape.js/unstable/documentation/img/tokyo-big.png" width="300" height="126">
 
-<img style="width: 300px; height: 126px;" src="https://raw.githubusercontent.com/cytoscape/cytoscape.js/unstable/documentation/img/tokyo-big-zoomed-in.png" width="300" height="126"></img>
+<img style="width: 300px; height: 126px;" src="https://raw.githubusercontent.com/cytoscape/cytoscape.js/unstable/documentation/img/tokyo-big-zoomed-in.png" width="300" height="126">
 
 A [live demo](https://js.cytoscape.org/demos/tokyo-railways/) and [source code](https://github.com/cytoscape/cytoscape.js/tree/master/documentation/demos/tokyo-railways) are available for the Tokyo railway stations graph.  More demos are available in the [documentation](https://js.cytoscape.org/#demos).