docs: fix arithmetic wording in help text

src/cli.rs

@@ -163,7 +163,7 @@ fn build_command() -> Command {
                      string '{VAR}' in each command by the current parameter value.\n\n  \
                      Example:  hyperfine -P threads 1 8 'make -j {threads}'\n\n\
                      This performs benchmarks for 'make -j 1', 'make -j 2', …, 'make -j 8'.\n\n\
-                     To have the value increase following different patterns, use shell arithmetics.\n\n  \
+                     To have the value increase following different patterns, use shell arithmetic.\n\n  \
                      Example: hyperfine -P size 0 3 'sleep $((2**{size}))'\n\n\
                      This performs benchmarks with power of 2 increases: 'sleep 1', 'sleep 2', 'sleep 4', …\n\
                      The exact syntax may vary depending on your shell and OS."