Replace Webpacker with Shakapacker

Author: ahangarha

.github/ISSUE_TEMPLATE.md

@@ -12,11 +12,11 @@ Tell us what should happen
 Tell us what happens instead
 
 ### System configuration
-**Sprockets or Webpacker version**:
-**React-Rails version**:
-**Rect_UJS version**:
-**Rails version**:
-**Ruby version**:
+- **Shakapacker or Sprockets version**:
+- **React-Rails version**:
+- **Rect_UJS version**:
+- **Rails version**:
+- **Ruby version**:
 
 
 -------

CONTRIBUTING.md

@@ -57,7 +57,7 @@ Include details about your configuration and environment, React-Rails integrates
 
 * **Which version of React-Rails are you using?**
 * **Which version of React_UJS are you using?**
-* **Which version of Webpacker/Sprockets are you using?**
+* **Which version of Shakapacker/Sprockets are you using?**
 * **Which version of Rails are you using?**
 
 ### Your First Code Contribution