Auto merge of #27481 - Monty0045:master, r=jdm

Support Linux Mint 20.04 for mach bootstrap

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Adds support for Linux Mint 20.04 (based on Ubuntu 20.04) to mach bootstrap.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors

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python/servo/bootstrap.py

@@ -339,7 +339,9 @@ def get_linux_distribution():
         else:
             major = version
 
-        if major == '19':
+        if major == '20':
+            base_version = '20.04'
+        elif major == '19':
             base_version = '18.04'
         elif major == '18':
             base_version = '16.04'