[Trivial] Grammar and typo correction

Minor corrections in src\test\* .

src/test/script_tests.cpp

@@ -465,7 +465,7 @@ public:
 std::string JSONPrettyPrint(const UniValue& univalue)
 {
     std::string ret = univalue.write(4);
-    // Workaround for libunivalue pretty printer, which puts a space between comma's and newlines
+    // Workaround for libunivalue pretty printer, which puts a space between commas and newlines
     size_t pos = 0;
     while ((pos = ret.find(" \n", pos)) != std::string::npos) {
         ret.replace(pos, 2, "\n");