use pixel tolerance for snapshot test

Example/Podfile

@@ -20,7 +20,7 @@ target 'Example' do
     target 'Application Specs' do
         inherit! :search_paths
         SwiftTestingPods()
-        pod 'Nimble-Snapshots'
+        pod 'Nimble-Snapshots', :git => 'https://github.com/paulz/Nimble-Snapshots.git', :branch => 'pixel-tolerance'
     end
 
     target 'OpenCV OSX Tests' do

Example/Podfile.lock

@@ -17,7 +17,7 @@ PODS:
 DEPENDENCIES:
   - ImageCoordinateSpace
   - Nimble
-  - Nimble-Snapshots
+  - Nimble-Snapshots (from `https://github.com/paulz/Nimble-Snapshots.git`, branch `pixel-tolerance`)
   - PerspectiveTransform (from `../`)
   - Quick
 
@@ -26,21 +26,28 @@ SPEC REPOS:
     - ImageCoordinateSpace
     - iOSSnapshotTestCase
     - Nimble
-    - Nimble-Snapshots
     - Quick
 
 EXTERNAL SOURCES:
+  Nimble-Snapshots:
+    :branch: pixel-tolerance
+    :git: https://github.com/paulz/Nimble-Snapshots.git
   PerspectiveTransform:
     :path: "../"
 
+CHECKOUT OPTIONS:
+  Nimble-Snapshots:
+    :commit: 472005cac0e5da082eb03f64fb41d61073b5d52f
+    :git: https://github.com/paulz/Nimble-Snapshots.git
+
 SPEC CHECKSUMS:
   ImageCoordinateSpace: 9e560a43a97375371f22343bb47e2c7e7fc428ae
   iOSSnapshotTestCase: 9ab44cb5aa62b84d31847f40680112e15ec579a6
   Nimble: 4ab1aeb9b45553c75b9687196b0fa0713170a332
-  Nimble-Snapshots: 8ec63f41ce6c7229a17be9a64edbc123b181f75b
+  Nimble-Snapshots: cc5ddfb60c5953242a71a1125d20998a8fc0f651
   PerspectiveTransform: 77d4f6b4ef5b8dbf5472afb8864ee3a74fffa193
   Quick: 7fb19e13be07b5dfb3b90d4f9824c855a11af40e
 
-PODFILE CHECKSUM: 1221c727f79e65c43c225a7da4f95a63cfa8f911
+PODFILE CHECKSUM: 7390b46646ad12744bbcb095521a2ea0d5d8fa4d
 
 COCOAPODS: 1.8.4

Example/Tests/SnapshotSpec.swift

@@ -42,6 +42,7 @@ class SnapshotSpec: QuickSpec {
                     let toleranceMessage = {"\(100 * tolerance)% tolerance"}
                     fputs("images are compared with \(toleranceMessage())\n".uppercased(), __stderrp)
                     expect(containerView).to(haveValidSnapshot(usesDrawRect: true,
+                                                               pixelTolerance: tolerance,
                                                                tolerance: tolerance),
                                              description: "should match with \(toleranceMessage())")
                 }