Saving PyPlot figure in julia code chunk in rBookdown

I can run the following code in Julia 1.2.0 console and it works fine - that is, it saves the figure as expected.

using PyPlot
clf();
ioff();
x1 = collect(0:0.1:2)
x2a = 1 .- 0.5x1
x2b = ifelse.(2 .- 2x1.>=0, 2 .- 2*x1,0)

fig, ax = subplots();

ax.fill_between(x1,x2a,color="red",linewidth=2,label=L"x_{2} \leq 1 - \frac{1}{2}x_{1}",alpha=0.3);
ax.legend(loc="upper right");
ax.fill_between(x1,x2b,color="blue",linewidth=2,label=L"x_{2} \leq 2 - 2x_{1}",alpha=0.3);
ax.legend(loc="upper right");
ax.set_xlabel(L"x_{1}")
ax.set_ylabel(L"x_{2}")
savefig("example-01a.png");

But when I run the same code inside a code chunk in rBookdown with Julia as the engine, the saved chart is blank, only showing the x-axis and y-axis.

using PyPlot
clf();
ioff();
x1 = collect(0:0.1:2)
x2a = 1 .- 0.5*x1
x2b = ifelse.(2 .- 2*x1.>=0, 2 .- 2*x1,0)

fig, ax = subplots();

ax.fill_between(x1,x2a,color="red",linewidth=2,label=L"x_{2} \leq 1 - \frac{1}{2}x_{1}",alpha=0.3);
ax.legend(loc="upper right");
ax.fill_between(x1,x2b,color="blue",linewidth=2,label=L"x_{2} \leq 2 - 2x_{1}",alpha=0.3);
ax.legend(loc="upper right");
ax.set_xlabel(L"x_{1}")
ax.set_ylabel(L"x_{2}")
savefig("example-01a.png");

My apologies if this is a trivial issue, and would appreciate any suggestions to address it.

Start by reproducing the Julia 1.2.0 PyPlot code in an rBookdown Julia code chunk and compare it with running the same code in the Julia console. The payload names no repository file or test, so trace JuliaCall's Julia-engine chunk execution and figure-saving path. Done means the generated example-01a.png contains the plotted filled regions, not only the axes.