Change the scriptstyle size from 2/3em to 0.7em

Summary:
I don't know why we originally used 2/3em for scriptstyle, but both TeX
and MathJax use 0.7em for the scriptstyle size.

Test Plan:
- Look at huxley tests, make sure everything that changed is due to the change
  in font size

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D12869

Style.js

@@ -63,8 +63,8 @@ var styles = [
     new Style(Dc, 0, 1.0, true),
     new Style(T, 1, 1.0, false),
     new Style(Tc, 1, 1.0, true),
-    new Style(S, 2, 0.66667, false),
-    new Style(Sc, 2, 0.66667, true),
+    new Style(S, 2, 0.7, false),
+    new Style(Sc, 2, 0.7, true),
     new Style(SS, 3, 0.5, false),
     new Style(SSc, 3, 0.5, true)
 ];

static/katex.less

@@ -151,15 +151,15 @@ big parens
     }
 
     .reset-textstyle.textstyle { font-size: 1em; }
-    .reset-textstyle.scriptstyle { font-size: 0.66667em; }
+    .reset-textstyle.scriptstyle { font-size: 0.7em; }
     .reset-textstyle.scriptscriptstyle { font-size: 0.5em; }
 
-    .reset-scriptstyle.textstyle { font-size: 1.5em; }
+    .reset-scriptstyle.textstyle { font-size: 1.42857em; }
     .reset-scriptstyle.scriptstyle { font-size: 1em; }
-    .reset-scriptstyle.scriptscriptstyle { font-size: 0.75em; }
+    .reset-scriptstyle.scriptscriptstyle { font-size: 0.71429em; }
 
     .reset-scriptscriptstyle.textstyle { font-size: 2em; }
-    .reset-scriptscriptstyle.scriptstyle { font-size: 1.5em; }
+    .reset-scriptscriptstyle.scriptstyle { font-size: 1.4em; }
     .reset-scriptscriptstyle.scriptscriptstyle { font-size: 1em; }
 
     .baseline-align-hack-outer() {