eslint: Add and enable space-unary-ops rule.

Info about rule at https://eslint.org/docs/rules/space-unary-ops.

.eslintrc.json

@@ -331,6 +331,7 @@
         // Updated regex expressions are currently being tested in casper
         // files and will decide about a potential future enforcement of this rule.
         "no-useless-escape": 0,
+        "space-unary-ops": 2,
         "no-whitespace-before-property": 2,
         "no-with": 2,
         "one-var": [ "error", "never" ],