Rename breakOnUnsupportedCmds to throwOnError.

Also, the MathBb-chrome test changed, to what I believe is the correct
result? Not sure why it looked wrong before.

Test plan:
 - `make test`
 - take screenshots, see nothing changed.

test/screenshotter/ss_data.js

@@ -11,7 +11,7 @@ var fs = require("fs");
 var jsyaml = require("js-yaml");
 var querystring = require("querystring");
 
-var queryKeys = ["tex", "pre", "post", "display", "doNotBreak", "errorColor"];
+var queryKeys = ["tex", "pre", "post", "display", "noThrow", "errorColor"];
 var dict = fs.readFileSync(require.resolve("./ss_data.yaml"));
 dict = jsyaml.safeLoad(dict);
 for (var key in dict) {

test/screenshotter/ss_data.yaml

@@ -106,7 +106,7 @@ SupSubOffsets: \displaystyle \int_{2+3}x f^{2+3}+3\lim_{2+3+4+5}f
 Text: \frac{a}{b}\text{c~ {ab} \ e}+fg
 UnsupportedCmds:
     tex: \err\,\frac\fracerr3\,2^\superr_\suberr\,\sqrt\sqrterr
-    doNotBreak: 1
+    noThrow: 1
     errorColor: "#dd4c4c"
 VerticalSpacing:
     pre: potato<br>blah

test/screenshotter/test.html

@@ -28,7 +28,7 @@
 
       var settings = {
           displayMode: !!query["display"],
-          breakOnUnsupportedCmds: !query["doNotBreak"]
+          throwOnError: !query["noThrow"]
       };
       if (query["errorColor"]) {
           settings.errorColor = query["errorColor"];