Fix modules with numbers in them.

Protoc ruby will output 'A2z' for package name 'a2z'.

protoc-gen-twirp_ruby/main.go

@@ -242,13 +242,9 @@ func camelCase(s string) string {
 	// case letter. Digits are treated as words.
 	for ; i < len(s); i++ {
 		c := s[i]
-		if c == '_' && i+1 < len(s) && isASCIILower(s[i+1]) {
+		if c == '_' && i+1 < len(s) && (isASCIILower(s[i+1]) || isASCIIDigit(s[i+1])) {
 			continue // Skip the underscore in s.
 		}
-		if isASCIIDigit(c) {
-			t = append(t, c)
-			continue
-		}
 		// Assume we have a letter now - if not, it's a bogus identifier. The next
 		// word is a sequence of characters that must start upper case.
 		if isASCIILower(c) {
@@ -256,7 +252,7 @@ func camelCase(s string) string {
 		}
 		t = append(t, c) // Guaranteed not lower case.
 		// Accept lower case sequence that follows.
-		for i+1 < len(s) && isASCIILower(s[i+1]) {
+		for i+1 < len(s) && (isASCIILower(s[i+1]) || isASCIIDigit(s[i+1])) {
 			i++
 			t = append(t, s[i])
 		}

protoc-gen-twirp_ruby/main_test.go

@@ -78,6 +78,8 @@ func TestCamelCase(t *testing.T) {
 		{camelCase("FooBar"), "FooBar"},
 		{camelCase("fooBar"), "FooBar"},
 		{camelCase("myLong_miXEDName"), "MyLongMiXEDName"},
+		{camelCase("a2z"), "A2z"},
+		{camelCase("a_2z"), "A2z"},
 	}
 	for _, tt := range tests {
 		if tt.expected != tt.actual {