matchers/cargo: Allow SPDX expressions

Using a regex that is similar to the one in
lib/licensee/matchers/spdx.rb in allowing spaces and parens.  Parens
aren't currently supported by Cargo's crates.io backing [1,2], but
that's hopefully a temporary limitation.  And Cargo/crates.io already
supports OR forms [3].

Ideally licensee would return the full license expression in these
cases instead of 'other' [4].  But since that conversion is happening
outside the matcher, this commit isn't making that any worse (although
it means this test isn't quite a unit test).

[1]: ehuss/license-exprs#3
[2]: rust-lang/cargo@c89dd64
[3]: rust-lang/cargo#4920
[4]: licensee#244

lib/licensee/matchers/cargo.rb

@@ -2,7 +2,7 @@ module Licensee
   module Matchers
     class Cargo < Licensee::Matchers::Package
       LICENSE_REGEX = %r{
-        ^\s*[\'\"]?license[\'\"]?\s*=\s*[\'\"]([a-z\-0-9\.+\/]+)[\'\"]\s*
+        ^\s*[\'\"]?license[\'\"]?\s*=\s*[\'\"]([a-z\-0-9\. +()\/]+)[\'\"]\s*
       }ix
 
       private

spec/licensee/matchers/cargo_matcher_spec.rb

@@ -17,14 +17,16 @@
   end
 
   {
-    'spdx name'          => ['license = "MIT"', 'mit'],
-    'single quotes'      => ["license = 'mit'", 'mit'],
-    'quoted key'         => ["'license' = 'mit'", 'mit'],
-    'double quoted key'  => ['"license"="mit"', 'mit'],
-    'no whitespace'      => ["license='mit'", 'mit'],
-    'leading whitespace' => [" license = 'mit'", 'mit'],
-    'other license'      => ['license = "Foo"', 'other'],
-    'multiple licenses'  => ['license = "Apache-2.0/MIT"', 'other']
+    'spdx name'                => ['license = "MIT"', 'mit'],
+    'single quotes'            => ["license = 'mit'", 'mit'],
+    'quoted key'               => ["'license' = 'mit'", 'mit'],
+    'double quoted key'        => ['"license"="mit"', 'mit'],
+    'no whitespace'            => ["license='mit'", 'mit'],
+    'leading whitespace'       => [" license = 'mit'", 'mit'],
+    'other license'            => ['license = "Foo"', 'other'],
+    'multiple licenses /'      => ['license = "Apache-2.0/MIT"', 'other'],
+    'multiple licenses OR'     => ['license = "Apache-2.0 OR MIT"', 'other'],
+    'multiple licenses parens' => ['license = "(Apache-2.0 OR MIT)"', 'other']
   }.each do |description, license_declaration_and_key|
     context "with a #{description}" do
       let(:content) { license_declaration_and_key[0] }