fix(challenges): fixed typo in css-grid.json (#46)

challenges/01-responsive-web-design/css-grid.json

@@ -857,7 +857,7 @@
       "tests": [
         {
           "text":
-            "<code>container</code> class should have a <code>grid-template-areas</code> propertiy similar to the preview but has <code>.</code> instead of the <code>advert</code> area.",
+            "<code>container</code> class should have a <code>grid-template-areas</code> property similar to the preview but has <code>.</code> instead of the <code>advert</code> area.",
           "testString":
             "assert(code.match(/.container\\s*?{[\\s\\S]*grid-template-areas\\s*?:\\s*?\"\\s*?header\\s*?header\\s*?header\\s*?\"\\s*?\"\\s*?.\\s*?content\\s*?content\\s*?\"\\s*?\"\\s*?footer\\s*?footer\\s*?footer\\s*?\"\\s*?;[\\s\\S]*}/gi), '<code>container</code> class should have a <code>grid-template-areas</code> propertiy similar to the preview but has <code>.</code> instead of the <code>advert</code> area.');"
         }