Unbreak spurious fails in gdb.base/step-line.exp

Unbreak spurious fails in gdb.base/step-line.exp

My copyright year update in the copyright headers of the step-line
testcase caused it to start failing, due to shift in line numbers.

    FAIL: gdb.base/step-line.exp: continue to f1
    FAIL: gdb.base/step-line.exp: next to dummy 2
    FAIL: gdb.base/step-line.exp: next over dummy 2
    FAIL: gdb.base/step-line.exp: step into f2
    FAIL: gdb.base/step-line.exp: next over dummy 4
    FAIL: gdb.base/step-line.exp: next to dummy 5
    FAIL: gdb.base/step-line.exp: next to dummy 6
    FAIL: gdb.base/step-line.exp: next over dummy 6
    FAIL: gdb.base/step-line.exp: next to dummy 7
    FAIL: gdb.base/step-line.exp: next to dummy 8
    FAIL: gdb.base/step-line.exp: next over dummy 8
    FAIL: gdb.base/step-line.exp: next to dummy 9
    FAIL: gdb.base/step-line.exp: next to dummy 10
    FAIL: gdb.base/step-line.exp: next over dummy 10

This was caused by the copyright.py script after I changed it to
also update this testcase, which made the following transformation:

    -   Copyright (C) 2001-2017
    -   Free Software Foundation, Inc.
    +   Copyright (C) 2001-2018 Free Software Foundation, Inc.

We can easily unbreak the testcase without having to go back to
manual edits each year by adding an extra line in the header.

gdb/testsuite/ChangeLog:

	* gdb.base/step-line.c: Add extra empty line in copyright header.
        * gdb.base/step-line.inp: Likewise.

Tested on x86_64-linux.