Adjust locations of files in comments. (#958)

[no important files changed]

exercises/practice/hello-world/hello_world.h

@@ -8,7 +8,7 @@
 // 'const char *', i.e. a pointer to a character (in this case the first
 // character in a string). The function itself is defined in the hello_world.c
 // source file. This function is called by the test case(s) in the test source
-// file test/test_hello_world.c.
+// file test_hello_world.c.
 const char *hello(void);
 
 #endif

exercises/practice/hello-world/test_hello_world.c

@@ -20,7 +20,7 @@ static void test_say_hi(void)
    // Check if the 'hello()' function returns "Hello, World!"
    // This test is expected to fail after first downloading this exercise.
    // To make this test pass, fix the 'hello()' function definition in the
-   // source file src/hello_world.c.
+   // source file hello_world.c.
    TEST_ASSERT_EQUAL_STRING("Hello, World!", hello());
 }