[mode/meta] Recognize Bazel, Buck and Pants build files as Python in mode/meta.js

BUCK, BUILD, *.BUILD and *.bzl files are build files for the three build
systems mentioned, and they are all valid Python files.

Author: Dominator008

mode/meta.js

@@ -105,7 +105,7 @@
     {name: "PowerShell", mime: "application/x-powershell", mode: "powershell", ext: ["ps1", "psd1", "psm1"]},
     {name: "Properties files", mime: "text/x-properties", mode: "properties", ext: ["properties", "ini", "in"], alias: ["ini", "properties"]},
     {name: "ProtoBuf", mime: "text/x-protobuf", mode: "protobuf", ext: ["proto"]},
-    {name: "Python", mime: "text/x-python", mode: "python", ext: ["py", "pyw"]},
+    {name: "Python", mime: "text/x-python", mode: "python", ext: ["BUILD", "bzl", "py", "pyw"], file: /^(BUCK|BUILD)$/},
     {name: "Puppet", mime: "text/x-puppet", mode: "puppet", ext: ["pp"]},
     {name: "Q", mime: "text/x-q", mode: "q", ext: ["q"]},
     {name: "R", mime: "text/x-rsrc", mode: "r", ext: ["r"], alias: ["rscript"]},