Update README.md

Made explicit HTTPS calls

Author: alanyee

README.md

@@ -1,14 +1,14 @@
 SICP
 ====
 
-<img src="http://sicpebook.files.wordpress.com/2013/09/smile0.png"
+<img src="https://sicpebook.files.wordpress.com/2013/09/smile0.png"
  alt="Par smiling" align="right" />
 
-This is a new HTML5 and EPUB3 version of "Structure and Interpretation of Computer Programs" by Abelson, Sussman, and Sussman. It comes from the lineage of [Unofficial Texinfo Format](http://www.neilvandyke.org/sicp-texi/) that was converted from the original [HTML version](http://mitpress.mit.edu/sicp/) at The MIT Press.
+This is a new HTML5 and EPUB3 version of "Structure and Interpretation of Computer Programs" by Abelson, Sussman, and Sussman. It comes from the lineage of [Unofficial Texinfo Format](http://www.neilvandyke.org/sicp-texi) that was converted from the original [HTML version](https://mitpress.mit.edu/sicp) at The MIT Press.
 
 <b>In EPUB3 format: [sicp.epub](https://github.com/sarabander/sicp-epub/blob/master/sicp.epub?raw=true)</b>
 
-<b>For online reading: [HTML book](http://sarabander.github.io/sicp/)</b>
+<b>For online reading: [HTML book](https://sarabander.github.io/sicp)</b>
 
 Modern solutions such as scalable vector graphics, mathematical markup with MathML and MathJax, embedded web fonts, and syntax highlighting are used. Rudimentary scaffolding for responsive design is in place, which adapts the page for viewing on pocket devices and tablets. More tests on small screens are needed to adjust the font size and formatting, so I encourage feedback from smartphone and tablet owners.
 
@@ -23,7 +23,7 @@ $ make
 
 All the files in `html` directory, but not in subdirectories, will be overwritten, so the preferred place to make changes is `sicp-pocket.texi.` The EPUB file will be created in the parent directory, outside of the project tree.
 
-You will need [Texinfo 5.1](http://ftp.gnu.org/gnu/texinfo/), Perl 5.12 or later, Ruby 1.9.3 or newer, [Nokogiri](http://nokogiri.org/) gem, [PhantomJS](http://phantomjs.org/), and Internet connection to compile the book.
+You will need [Texinfo 5.1](https://ftp.gnu.org/gnu/texinfo), Perl 5.12 or later, Ruby 1.9.3 or newer, [Nokogiri](http://nokogiri.org) gem, [PhantomJS](http://phantomjs.org), and Internet connection to compile the book.
 
 Acknowledgements
 ----------------
@@ -39,7 +39,7 @@ Acknowledgements
 License
 -------
 
-The source file `sicp-pocket.texi,` HTML content of the book, and diagrams in directory `html/fig` are licensed under Creative Commons Attribution-ShareAlike 4.0 International License ([cc by-sa](http://creativecommons.org/licenses/by-sa/4.0/)).
+The source file `sicp-pocket.texi,` HTML content of the book, and diagrams in directory `html/fig` are licensed under Creative Commons Attribution-ShareAlike 4.0 International License ([cc by-sa](https://creativecommons.org/licenses/by-sa/4.0)).
 
 Most of the scripts are licensed under GNU General Public License version 3 (for details, see LICENSE.src).