Fix #where for hashes with string keys

lib/active_hash/base.rb

@@ -411,7 +411,7 @@ def [](key)
     end
 
     def _read_attribute(key)
-      attributes[key]
+      attributes[key.to_sym]
     end
     alias_method :read_attribute, :_read_attribute
 

spec/active_hash/base_spec.rb

@@ -284,6 +284,13 @@ class Region < ActiveHash::Base
       expect(record.first.name).to eq('US')
     end
 
+    it "filters records when passed a hash with string keys" do
+      record = Country.where('name' => 'US')
+      expect(record.count).to eq(1)
+      expect(record.first.id).to eq(1)
+      expect(record.first.name).to eq('US')
+    end
+
     it "raises an error if ids aren't unique" do
       expect do
         Country.data = [
@@ -1194,12 +1201,24 @@ class Region < ActiveHash::Base
       expect(country._read_attribute(:foo)).to eq(:bar)
     end
 
+    it "works when string key passed to _read_attribute" do
+      Country.field :foo
+      country = Country.new(:foo => :bar)
+      expect(country._read_attribute('foo')).to eq(:bar)
+    end
+
     it "works with read_attribute" do
       Country.field :foo
       country = Country.new(:foo => :bar)
       expect(country.read_attribute(:foo)).to eq(:bar)
     end
 
+    it "works when string key passed to read_attribute" do
+      Country.field :foo
+      country = Country.new(:foo => :bar)
+      expect(country.read_attribute('foo')).to eq(:bar)
+    end
+
     it "works with #[]=" do
       Country.field :foo
       country = Country.new