Update image source for battery charging profile

Updated image source in README and removed local image reference.

Author: robertogl

Classroom Challenge Projects/Projects/Modeling and Optimizing a Battery Charging Profile/README.md

@@ -1,11 +1,7 @@
 <table>
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-<td><img src=" BatteryCharge.png"  width=500 /></td>
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+<td><img src="https://gist.githubusercontent.com/robertogl/e0115dc303472a9cfd52bbbc8edb7665/raw/BatteryCharge.png"  width=500 /></td>
 <td><p><h1>Modeling and Optimizing a Battery Charging Profile</h1></p>
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 <p>Use MATLAB to model a lithium battery-charging profile</p>
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 </table>
 
 ## Motivation