Add riscv32 and riscv64 support (#62)

Motivation:

- `os-maven-plugin` doesn't recognize the following `os.arch` values:
  - `riscv32`
  - `riscv64`

Modifications:

- Return `riscv` for `riscv` and `riscv32`.
- Return `riscv64` for `riscv64`.

Result:
- Fixes #61

Co-authored-by: Trustin Lee <t@motd.kr>

README.md

@@ -44,7 +44,8 @@
 * `ppcle_64` - if the value is `ppc64le`
 * `s390_32` - if the value is `s390`
 * `s390_64` if the value is `s390x`
-* `riscv` if the value is `riscv`
+* `riscv` if the value is `riscv` or `riscv32`
+* `riscv64` if the value is `riscv64`
 * `e2k` if the value is `e2k`
 
 Note: The bitness part of this property relies on the bitness of the JVM binary, e.g. You'll get the property that ends with `_32` if you run a 32-bit JVM on a 64-bit OS.

src/main/java/kr/motd/maven/os/Detector.java

@@ -245,9 +245,12 @@ private static String normalizeArch(String value) {
         if ("s390x".equals(value)) {
             return "s390_64";
         }
-        if ("riscv".equals(value)) {
+        if (value.matches("^(riscv|riscv32)$")) {
             return "riscv";
         }
+        if ("riscv64".equals(value)) {
+            return "riscv64";
+        }
         if ("e2k".equals(value)) {
             return "e2k";
         }