Fixes path truncation in PathMiddlewareDecorator to be case insensitive

In #168, we received a report indicating that path matching within
`PathMiddlewareDecorator` fails if the path is the same, but using a
different case.

Interestingly, we _match_ it correctly; the problem is when _preparing
the truncated path_ to pass on to the decorated middleware, as it cannot
identify the matched segment correctly.

This patch modifies the logic in `getTruncatedPath()` to do a
case-insensitive comparison of the segment and the path in the initial
condition.

src/Middleware/PathMiddlewareDecorator.php

@@ -108,7 +108,7 @@ private function prepareRequestWithTruncatedPrefix(ServerRequestInterface $reque
      */
     private function getTruncatedPath($segment, $path)
     {
-        if ($segment === $path) {
+        if (strtolower($segment) === strtolower($path)) {
             // Decorated path and current path are the same; return empty string
             return '';
         }

test/Middleware/PathMiddlewareDecoratorTest.php

@@ -394,4 +394,30 @@ public function testUpdatesInPathInsideNestedMiddlewareAreRespected()
 
         $this->assertSame($response, $middleware->process($request, $handler->reveal()));
     }
+
+    public function testProcessesMatchedPathsWithoutCaseSensitivity()
+    {
+        $finalHandler = $this->prophesize(RequestHandlerInterface::class);
+        $finalHandler->{HANDLER_METHOD}(Argument::any())->willReturn(new Response());
+
+        // Note that the path requested is ALL CAPS:
+        $request  = new ServerRequest([], [], 'http://local.example.com/MYADMIN', 'GET', 'php://memory');
+
+        $middleware = $this->prophesize(MiddlewareInterface::class);
+        $middleware
+            ->process(
+                Argument::that(function (ServerRequestInterface $req) {
+                    Assert::assertSame('', $req->getUri()->getPath());
+
+                    return true;
+                }),
+                Argument::any()
+            )
+            ->willReturn(new Response())
+            ->shouldBeCalledTimes(1);
+
+        // Note that the path to match is lowercase:
+        $decorator = new PathMiddlewareDecorator('/myadmin', $middleware->reveal());
+        $decorator->process($request, $finalHandler->reveal());
+    }
 }