Fix tldp.org links

Link on tldp.org seems to be down right now, but www.tldp.org seems to work.
Also, switch them to https while we're at it.

Author: iddecker

mkdocs/docs/HPC/linux-tutorial/beyond_the_basics.md

@@ -303,7 +303,7 @@ commands you put in there will be executed from the top to bottom.
 
 However, there are some rules you need to abide by.
 
-Here is a [very detailed guide](http://www.tldp.org/LDP/Bash-Beginners-Guide/html/) should you
+Here is a [very detailed guide](https://www.tldp.org/LDP/Bash-Beginners-Guide/html/) should you
 need more information.
 
 ### Shebang
@@ -357,7 +357,7 @@ brackets, the **then** needs to be at the beginning of a line. It is best to jus
 copy this example and modify it.
 
 In the initial example, we used `-d` to test if a directory existed.
-There are [several more checks](http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html).
+There are [several more checks](https://www.tldp.org/LDP/Bash-Beginners-Guide/html/sect_07_01.html).
 
 Another useful example, is to test if a variable contains a value (so it's
 not empty):

mkdocs/docs/HPC/linux-tutorial/common_pitfalls.md

@@ -143,13 +143,13 @@ smallest of problems!**
     examples. There is an associated book which gets a lot of good
     reviews
 
-3.  [The Linux Documentation Project](http://www.tldp.org/guides.html): More guides on various topics relating to the Linux command line
+3.  [The Linux Documentation Project](https://www.tldp.org/guides.html): More guides on various topics relating to the Linux command line
 
 4.  [basic shell
     usage](http://linuxcommand.org/lc3_learning_the_shell.php)
 
 5.  [Bash for
-    beginners](http://www.tldp.org/LDP/Bash-Beginners-Guide/html/Bash-Beginners-Guide.html)
+    beginners](https://www.tldp.org/LDP/Bash-Beginners-Guide/html/Bash-Beginners-Guide.html)
 
 6.  [MOOC](https://www.edx.org/course/introduction-linux-linuxfoundationx-lfs101x-0)
 

mkdocs/docs/HPC/linux-tutorial/getting_started.md

@@ -194,7 +194,7 @@ empty variables are used. (see <https://ss64.com/bash/set.html> for
 a more detailed explanation and more options)
 
 More information can be found at
-<http://www.tldp.org/LDP/abs/html/variables.html>.
+<https://www.tldp.org/LDP/abs/html/variables.html>.
 
 ### Restoring your default environment