Simplified docker building

Dockerfile

@@ -1,21 +1,13 @@
 FROM alpine:3.19.1
 
-RUN apk add make g++
+RUN apk add --no-cache make=4.4.1-r2 g++=13.2.1_git20231014-r0 \
+	&& adduser --disabled-password saundersp
+
+USER saundersp
 
 WORKDIR /home/saundersp/sorting_algorithms
 
-RUN adduser \
-	--disabled-password \
-	--gecos '' \
-	--home "$(pwd)" \
-	--no-create-home \
-	saundersp
-
-COPY . .
-
-RUN chown -R saundersp /home/saundersp/sorting_algorithms
-
-USER saundersp
+COPY *.cpp *.hpp Makefile ./
 
 RUN make -j "$(nproc)"