Xcode 10 support

This PR temporarily disables dark mode support for Xcode 10 until the views can be fully revised to support dark mode on Mojave, in a later Tulsi.

This PR also removes the use of a range constructor that turns out to be wholly unnecessary, as the half open range operator already creates a Swift Range. It breaks the build in Xcode 10. That might have been an artifact in going from NSRanges to Swift Ranges in TulsiGenerator.

Closes #53.

PiperOrigin-RevId: 206004931
diff --git a/src/Tulsi/Info.plist b/src/Tulsi/Info.plist
index 0f090df..1f3bd9f 100644
--- a/src/Tulsi/Info.plist
+++ b/src/Tulsi/Info.plist
@@ -85,6 +85,8 @@
 	<string>Main</string>
 	<key>NSPrincipalClass</key>
 	<string>NSApplication</string>
+	<key>NSRequiresAquaSystemAppearance</key>
+	<true/>
 	<key>UTExportedTypeDeclarations</key>
 	<array>
 		<dict>
diff --git a/src/TulsiGenerator/BuildLabel.swift b/src/TulsiGenerator/BuildLabel.swift
index 1f8e74d..62467bc 100644
--- a/src/TulsiGenerator/BuildLabel.swift
+++ b/src/TulsiGenerator/BuildLabel.swift
@@ -37,7 +37,7 @@
     }
 
     if package.hasPrefix("//") {
-      package.removeSubrange(Range(package.startIndex ..< package.index(package.startIndex, offsetBy: 2)))
+      package.removeSubrange(package.startIndex ..< package.index(package.startIndex, offsetBy: 2))
     }
     if package.isEmpty || package.hasSuffix("/") {
       return ""