Fix to error at comparing signed and unsigned integers (#97)

In animation_tests.cpp Frame.index (which is signed integer) is
compared with integer literals with 'u' at the end, making them unsigned
integers. GCC6.x treats such comparison as error (at least with flags
set in CMakeLists.txt). This patch just removes 'u' from literals,
allowing the build to pass with GCC6.

Author: Erdk

src/tests/unit_tests/animation_tests.cpp

@@ -11,7 +11,7 @@ using namespace jet;
 
 TEST(Frame, Constructors) {
     Frame frame;
-    EXPECT_EQ(0u, frame.index);
+    EXPECT_EQ(0, frame.index);
     EXPECT_DOUBLE_EQ(1.0 / 60.0, frame.timeIntervalInSeconds);
 }
 
@@ -32,15 +32,15 @@ TEST(Frame, Advance) {
         frame.advance();
     }
 
-    EXPECT_EQ(54u, frame.index);
+    EXPECT_EQ(54, frame.index);
 
     frame.advance(23);
 
-    EXPECT_EQ(77u, frame.index);
+    EXPECT_EQ(77, frame.index);
 
-    EXPECT_EQ(78u, (++frame).index);
+    EXPECT_EQ(78, (++frame).index);
 
-    EXPECT_EQ(78u, (frame++).index);
+    EXPECT_EQ(78, (frame++).index);
 
-    EXPECT_EQ(79u, frame.index);
+    EXPECT_EQ(79, frame.index);
 }