docs fix spelling issues (#329)

* Update SECURITY.md

* Update test_shape_cs.rs

* Update bignat.rs

SECURITY.md

@@ -12,7 +12,7 @@ If you believe you have found a security vulnerability in any Microsoft-owned re
 
 Instead, please report them to the Microsoft Security Response Center (MSRC) at [https://msrc.microsoft.com/create-report](https://msrc.microsoft.com/create-report).
 
-If you prefer to submit without logging in, send email to [secure@microsoft.com](mailto:secure@microsoft.com).  If possible, encrypt your message with our PGP key; please download it from the [Microsoft Security Response Center PGP Key page](https://www.microsoft.com/en-us/msrc/pgp-key-msrc).
+If you prefer to submit without logging in, send an email to [secure@microsoft.com](mailto:secure@microsoft.com).  If possible, encrypt your message with our PGP key; please download it from the [Microsoft Security Response Center PGP Key page](https://www.microsoft.com/en-us/msrc/pgp-key-msrc).
 
 You should receive a response within 24 hours. If for some reason you do not, please follow up via email to ensure we received your original message. Additional information can be found at [microsoft.com/msrc](https://www.microsoft.com/msrc). 
 
@@ -38,4 +38,4 @@ We prefer all communications to be in English.
 
 Microsoft follows the principle of [Coordinated Vulnerability Disclosure](https://www.microsoft.com/en-us/msrc/cvd).
 
-<!-- END MICROSOFT SECURITY.MD BLOCK -->
+<!-- END MICROSOFT SECURITY.MD BLOCK -->

src/bellpepper/test_shape_cs.rs

@@ -133,7 +133,7 @@ where
     result
   }
 
-  /// Print all iputs and a detailed representation of each constraint.
+  /// Print all inputs and a detailed representation of each constraint.
   #[allow(dead_code)]
   pub fn pretty_print(&self) -> String {
     let mut s = String::new();

src/gadgets/nonnative/bignat.rs

@@ -356,7 +356,7 @@ impl<Scalar: PrimeField> BigNat<Scalar> {
   ) -> Result<(), SynthesisError> {
     self.enforce_limb_width_agreement(other, "equal_when_carried")?;
 
-    // We'll propegate carries over the first `n` limbs.
+    // We'll propagate carries over the first `n` limbs.
     let n = min(self.limbs.len(), other.limbs.len());
     let target_base = BigInt::from(1u8) << self.params.limb_width as u32;
     let mut accumulated_extra = BigInt::from(0usize);