Solution (source code)

= Solution

\b[True.] Given $\varepsilon>0$, <uniform continuity> supplies $\delta>0$ such that $|x-y|<\delta$ implies $|f(x)-f(y)|<\varepsilon$. For all sufficiently large $n$, $1/n<\delta$, and then
$$
\sup_{x\in\mathbb R}|f(x+1/n)-f(x)|<\varepsilon.
$$
This is precisely <uniform convergence> of $f_n$ to $f$.